Eric Sembrat's Test Bonanza

Lipid based membranes are an essential building block of all cellular life, separating the inside of a cell from the outside and compartmentalizing the cell interior. Once thought of as passive and featureless environments for membrane proteins, a new picture of bio-membranes has begun to emerge that paints them as structured, complex fluids whose proper dynamic organization plays an important role in cellular life. Our studies combine optical microscopy, spectroscopy biochemical techniques to uncover some of the physical and chemical mechanism that lead to dynamic organization of the lipid membrane interfaces and its constituents. Particular attention is thereby given to the interactions of calcium ions and phosphoinositides- an important class of signaling lipids-as well as regulation of the spectrin based membrane skeleton in mechanotransduction. In addition, possible implications of structured, fluid membrane interfaces for biomimetic systems in bio- and nanotechnology are explored.

Movement is a defining characteristic of animals. They have evolved a diversity of successful
movement strategies where responsiveness to their surroundings is paramount and perturbations are
the norm. My research program seeks to understand the physiological basis of a central challenge for
animals: the generation of stable, versatile locomotion through complex environments. Locomotion
arises through the interplay of multiple physiological systems acting in the context of an organism’s
interactions with it environment. A central task for animals during locomotion is acquiring, processing,
transforming and acting upon information. Yet nervous systems of animals must operate through the
physics of sensors and actuators to interface with the environment. Understanding how
neurophysiology, biomechanics and muscle physiology combine to shape locomotion demands an
approach that draws upon computational and analytical tools from the physical, mathematical and
engineering disciplines to complement a comparative experimental biology program: an integrative
science of biological movement.

We will present a simple non-relativistic model to describe the low energy excitations of graphene. Our model is based on a deformation of the Heisen-
berg algebra in such a way that the commutator of momenta is proportional to the pseudo-spin. We solve the Landau problem for the resulting Hamil-
tonian, which reduces in the large mass limit, while keeping constant the Fermi velocity, to the usual linear one employed to describe these excitations
as massless Dirac fermions. Extending this model to negative mass we re-produce the leading mass term in the low energy expansion of the dispersion relation for both nearest and next-to-nearest-neighbor interactions. Taking into account the contribution from both Dirac points, we evaluate the Hall conductivity with a zeta-function approach. The result is consistent with the anomalous integer quantum Hall eect in graphene. The idea is to present also a short introduction to non-commutative quantum mechanics.
 

The hydrologic cycle is an exquisitely coordinated, balanced, interaction between the atmosphere, the oceans, and the land that controls, among other things, the planet’s temperature by moving large quantities of matter and energy. The system is incredibly complex with a myriad of positive and negative feedbacks acting at a variety of scales. Much of what we experience in our natural and altered environments results from these complex interactions. Surprisingly (or maybe not) this complexity many times results in beautifully organized expressions of the hydrologic state that are commonly amenable to fairly simple explanations.

 This talk explores some outcomes of hydrologic complexity and organization. Topics include the impact of soil moisture on the atmosphere and vice-versa, the impact of deforestation on the Amazon cloud climate, the self-organization of landscapes and river basins over very long time periods and the roles of vegetation on landscape evolution and in turn the role of the landscape on vegetation distribution.

For over 200 years, the metric system has been the standard for comparing measurements in science and industry. Formal procedures were adopted about 125 years ago to create the International System (SI) of units, and it has been steadily improved. In the next few years, the SI will be completely redefined to make all units more reproducible for the foreseeable future. The base concepts of time, length, mass, charge, temperature, amount of substance, and luminosity will have SI units of seconds, meters, kilograms, coulombs, kelvins, moles, and candela, respectively, all linked to fundamental physical constants.

Conducting tests to obtain consistent and better values for physics constants has a long history, going back to Galileo trying to measure the speed of light. Many physics constants now have values in SI units of 8 digits or more, but that accuracy improved slowly. The Planck constant h has the shortest history of them all, since it was only conceived in the modern quantum approach to atomic theory. This talk will use the Planck constant as an example of how the uncertainty in constants measurements decreases, but not without jumps and disagreements, even increasingly smaller ones, that still have significant effects.

Change always involves controversy. The early Planck values “quickly” changed by one percent as physics itself developed. Even in the 1970's and 80's there was controversy over voltage units, arising in the changeover from standard chemical cells to the quantum-based Josephson effect. Today's hot topic concerns changing from the last artifact, a kilogram mass standard, to a Planck constant (or Avogadro constant) definition. The recent discrepancies over Planck and Avogadro results are a factor of 100 smaller than those over voltage, showing how electronic metrology is still progressing, and that research on accurate measurements is never complete.

The mechanisms governing the transfer of pathogens between infected and non-infected members of a population are critical in shaping the outcome of an epidemic. This is true whether one considers human, animal or plant populations. Despite major efforts to investigate the large-scale population-level disease dynamics and the micro-scale pathogen-level dynamics, the fundamental mechanisms of transmission of most pathogens remain poorly understood. A critical gap in our understanding of the bridge between population-level and pathogen-level mechanisms persists. Drawing upon clinical data, fluid experiments and theoretical modeling I will discuss the dynamics of transmission of various pathogens through the lens of fundamental fluid dynamics.

Biography:

Lydia Bourouiba is a physical applied mathematician working on fundamental fluid mechanics problems at the interface of epidemiology and fluid dynamics. She completed her Ph.D. from McGill University in November 2008, studying rotating homogeneous turbulence theoretically and numerically. She was then an NSERC Postdoctoral Fellow in applied mathematics at the Centre for Disease Modelling of Toronto. There, she examined the modes of transmission of avian influenza. She then continued her postdoctoral research at MIT as an NSERC Fellow and Instructor in the Department of Mathematics where she joined the Applied Math Fluid Laboratory in 2010. There, she merged her two scientific backgrounds and combined theory and experiments to identify and elucidate modes of infectious disease transmission where fluids are ubiquitous.

NASA has followed the water on Mars, and has now progressed further to asking: is or was this environment ever actually habitable by life as we know it?  All such life has some common physical and chemical requirements, which we can look for via orbital remote sensing and missions to the Martian surface.  Recent results from the Curiosity rover are providing a delightfully nuanced answer to this question.  The talk will discuss how we arrived at Gale crater (versus the many other interesting places on Mars), what we have been doing there, and what we must do beyond Curiosity to answer our most fundamental questions about how the Martian environment has evolved over time.

Understanding dynamics of pattern formation, following a symmetry breaking quantum phase transition is an area of active interest. Spontaneous spin domain is formed in sodium Bose-Einstein condensates that are quenched, i.e. rapidly tuned, through a quantum phase transition from polar to antiferromagnetic phases. A microwave ``dressing'' field globally shifts the energy of the m_F= 0 level below the average of the m_F= ±1 energy levels, inducing a dynamical instability . We use local spin measurements to quantify the spatial ordering kinetics in the vicinity of the phase transition. For an elongated BEC, the instability nucleates small antiferromagnetic domains near the center of the polar condensate that grow in time along one spatial dimension. After a rapid nucleation and coarsening phase, the system exhibits long timescale non-equilibrium dynamics without relaxing to a uniform antiferromagnetic phase.

Atoms in optical lattices are very versatile experimental systems. They can be used to study many-body quantum physics, to aid
precision measurements and tests of fundamental symmetries, and for quantum computation. I will describe ongoing efforts along these lines
in my research group.

The rich astronomy of gravitational radiation is being intensively prepared using sophisticated analytic calculations, massive numerical simulations, and incredibly sensitive experimental facilities. These different approaches must work closely together if we are to use gravitational waves to understand the universe. Already, before the first direct detections of gravitational waves, we understand much more than a decade ago about the fascinating dynamical geometry of black holes and about the physics of how gravitational radiation is generated. Meanwhile the technologies being developed for detection promise applications across the rest of physics. The detections that are expected in the next few years, using the LIGO system and then expanding it into a worldwide network of 5 or more large interferometers, will allow us to test general relativity in radical new ways and to explore the astrophysics of highly relativistic systems. In the longer term, a space-based detector like the super-sensitive LISA will survey the supermassive black hole population of the universe back to the epoch where galaxies were first forming, thereby identifying and studying the earliest discrete objects that have ever been observed in astronomy.