Integrated Calendar

Flying insects can perform a wide array of extreme aerial maneuvers with exquisite accuracy and robustness, outmaneuvering any man-made flying device. As a physical system, a flapping insect is strongly nonlinear with fast-growing mechanical instabilities that must be controlled to allow flight. Hence, similar to balancing a stick on one's fingertip, flapping flight is a delicate balancing act made possible only by ever-present, fast corrective actions. Understanding the underlying mechanisms of insect flight is a major challenge, since this graceful behavior is highly coupled to complex fluid flows and arises from the concerted operation of physiological functions across multiple length and time scales. As such, Insect flight research involves basic concepts from nonlinear dynamics, fluid mechanics, neurobiology and control theory, and has direct application to the development of small flapping robots.

Here we show how flies control their rotational degrees of freedom: yaw, pitch and roll. We focus on their body roll angle, which is unstable and most sensitive degree of freedom. We glue a magnet to each fly and apply a short magnetic pulse that rolls it in mid-air. Fast video shows that flies fully correct for perturbations of up to 100o within 30±7ms. The roll correction maneuver consists of a stroke-amplitude asymmetry that is well described by a linear PI controller. For more aggressive perturbations, we show evidence for nonlinear and hierarchical control mechanisms. Flies respond to roll perturbations within a single wing-beat, or 5ms, making this correction reflex one of the fastest in the animal kingdom.

The BCC phase of solid helium-4 has a gapped excitation mode, as revealed by inelastic neutron scattering experiments. This mode is unexpected, since BCC is a Bravais lattice and therefore acoustic modes are the only low-lying excitations expected in the harmonic solid. I will give a simple model for this new collective excitation based on the amplitude fluctuations of a quantum solid

Membrane proteins are an exciting class of biomacromolecules and play important roles in a variety of biological processes that are directly linked to major diseases including cancer, aging-related diseases, and infectious diseases. A complete understanding of their function can only be accomplished using high-resolution structures. In spite of recent developments in structural biology, membrane proteins continue to pose tremendous challenges to most biophysical techniques. A major area of research in my group is focused on the development of NMR techniques to study the dynamic structures of membrane bound proteins such as cytochrome b5, cytochrome P450 and cytochrome P450-reductase. In the first-half of my talk, I will present strategies to study the structure and dynamics of these challenging systems and also on the electron transfer mechanism that enables the enzymatic
function of P450. The accumulation of misfolded proteins is a hallmark feature in numerous human disorders such as blood diseases like sickle cell anemia, neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease, and metabolic diseases such as type II diabetes. Misfolded protein aggregates may deposit in tissues, can be intracellular, extracellular, or both. The conformational changes accompanying misfolding can result in disruption of the regular function of the protein or may result in a gain of function that is often associated with toxicity. Amyloid peptides represent a subset of misfolded proteins whose misfolded state shares unique characteristics. Our research group has been investigating the high-resolution structures of early amyloid intermediates, amyloid-membrane interaction and membrane disruption, and the interaction of polyphenols with amyloid proteins. In the second-half of my presentation, NMR structures of early intermediates of amyloid peptides, mechanisms of amyloid-induced membrane disruption, and amyloid inhibition by polyphenolic compounds will be discussed. Solid-state NMR results on the interaction of amyloid fibers with lipid bilayers, and novel NMR approaches to investigate amyloid formation will also be presented.
1. BBA Biomembranes 1768 (2007) 3235.
2. Acc. Chem. Res. 116 (2012) 3650.
3. Chem. Soc. Rev. 41 (2012) 608.