Eric Sembrat's Test Bonanza

Circadian clocks rely on the alternation of light and dark to synchronize to the day/night cycle. However, a consequence of weather fluctuations and seasonal variations is that the driving signal received by the clock is highly variable not only from one day to the next but also throughout the year, which may compromise robust entrainment.

The microscopic green alga Ostreococcus tauri has recently emerged as a promising circadian model in the green lineage. Its clock is based on a central loop featuring orthologs of Arabidopsis TOC1 and CCA1 clock genes, yet seems to have a simpler architecture than Arabidopsis. The analysis of expression data from these two core clock genes and mathematical modeling have unveiled a simple yet effective strategy to protect the clock from fluctuations in daylight intensity, effectively decoupling the clock from the external cycle when it is on time. Being robust to these fluctuations appears to be sufficiently important that this strategy can be clearly evidenced for all photoperiods between 2 and 22 hours, despite the fact that the expression profiles significantly depend on day duration. This shows that a circadian clock can be both robust and flexible, using simple principles from nonlinear oscillator physics.

The tidal disruption of a star can serve as a diagnostic for the presence of a dormant black hole in a distant galaxy.  While such tidal disruption events are rare, they give rise to powerful flares of emission at and above Eddington luminosity, with spectral features and timescales that might reveal both the type of star and the mass (and perhaps spin) of the black hole.  In our study, we consider relativistic encounters between white dwarfs and massive black holes at the threshold of disruption.  We develop a numerical code whose central feature is the use of Fermi normal coordinates (FNC).  We characterize the mass loss from the star and provide a detailed view into the (hydro)dynamics of the remnant and debris.  In this talk, I will discuss these results and present a hybrid approach that relies on the FNC method in combination with fully general relativistic hydrodynamics to model the early accretion of debris onto the black hole with high accuracy. This new and timely development in tidal disruption studies is directly motivated by the anticipated abundance of data from the current and upcoming multi-wavelength surveys of the transient sky.

Cosmic rays are microscopic, charged particles that permanently bombard Earth from outer space. 100 years after their discovery their origin is still a mystery. It is also not clear how cosmic rays can obtain energies that are sometimes billion times larger than what can be produced in the most powerful particle accelerator on Earth, the LHC, where the Higgs particle was discovered last year. Possible particle accelerators that nature provides are very exotic sites in the universe like exploding stars, massive black holes, gamma-ray bursts, and pulsars. To find out more about these enigmatic particles and their origin a number of experiments on ground and space have been put into operation over the past ten years and provide us with stunning results.  I will give an introduction to cosmic rays, how we detect them, what we have learned from recent measurements about the origin of cosmic rays, and how cosmic rays are used to test the foundation of modern physics.

To accept Special Relativity we give up Absolute Time. What do we give up to accept Quantum Theory?  After all these years Heisenberg's 1925 discovery paper for Quantum Theory is still opaque, in contrast to  Einstein's for Special Relativity. In hindsight, to accept Quantum Theory we must give up the Classical Principle, which is hardly ever even stated, for the Quantum Principle.  Today this is naturally inferred from a well-known polarization study of Malus in 1805.  Problems  like "spooky action at a distance", ``state vector collapse",  and the Einstein-Podolsky-Rosen "paradox" are penalties for  disrespecting the Quantum Principle.  If Time permits,  I will quantize him too.

Have you ever wondered why an egg solidifies at high temperature while most pure substances, like water, do not? Or why materials solely made of liquids can exhibit solid-like properties? Or why adding a tiny amount of certain additives to water dramatically changes the way water flows? This talk will touch on some of these aspects. It will start by discussing what soft condensed matter is and why soft materials are indeed soft. It will then briefly discuss viscous flow, to end introducing the significance of phase transformations in manipulating food. The aim of the talk is to inspire you into thinking about the properties and behavior of food, while illustrating the power of physics for rationalizing some of the fascinating diversity exhibited by the materials we eat.

I introduce a class of dynamical systems which exhibit motion in their lowest-energy states and thus spontaneously break time-translation symmetry. Their Lagrangians have nonstandard kinetic terms and their Hamiltonians are multivalued functions of momentum, yet they are perfectly consistent and amenable to quantization.  Possible  applications to condensed matter systems and cosmology will be discussed.

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Our Milky Way is a beautiful spiral galaxy and has been constantly growing since the beginning of time.  How did the ancestors of the Milky Way form and look in the first billion years of the universe? Before galaxies form, isolated massive stars ignite from primordial gas composed of only hydrogen and helium.  They forever changed the cosmic landscape by heating their surroundings and enriching the universe with the first heavy elements.  These events spark the era of galaxy formation, where dwarf galaxies assemble first and then merge together to form larger and larger galaxies.  Observations from the Hubble Space Telescope are just now uncovering these baby galaxies, and a wealth of information will come from the James Webb Space Telescope, due to launch in 2018.  Supercomputer simulations of galaxy formation are vital to interpret these data and to learn about our cosmic origins.  In my talk, I will present the latest results of supercomputer simulations that reveal the sequence of events that lead to the birth of the first galaxies in the universe.

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Combining knowledge of physics with a healthy willingness to estimate and approximate, we can say some rather profound things about future paths available to our society in terms of energy and resources.  Topics such as growth, global warming, fossil fuels and their potential replacements, and energy storage are ripe targets for back-of-the-envelope quantification, and will be explored in this talk.  A subtext is that we should not take 

for granted that superior substitutes will replace fossil fuels.

I will discuss three fluid-mechanics problems: fluid motions related to drinking, clapping, and bouncing, which you might have experienced or observed once during daily activities.

Drinking: Drinking is defined as the animal action of taking water into the mouth, but to fluid mechanists, is simply one kind of fluid transport phenomena. Classical fluid mechanics show that fluid transport can be achieved by either pressure-driven or inertia-driven processes. In a similar fashion, animals drink water using pressure-driven or inertia-driven mechanisms. For example, domestic cats and dogs lap water by moving the tongue fast, thereby developing the inertia-driven mechanism. We will investigate how cats and dogs drink water differently and discuss the underlying fluid mechanics.

Clapping: Droplets splash around when a fluid volume is quickly compressed. This phenomenon has been observed during common activities such as kids clapping with wet hands. The underlying mechanism involves a fluid volume being compressed vertically between two objects. This compression causes the fluid volume to be ejected radially and thereby generate fluid threads and droplets at a high speed. In this study, we designed and performed laboratory experiments to observe the process of thread and drop formation after a fluid is squeezed.

Bouncing: When two fluid jets collide, they can bounce off each other, due to a thin film of air which keeps them separated. We describe the stable non-coalescence phenomenon between two jets of the same fluid, colliding obliquely with each other. Using a simple experimental setup, we carry out a parametric study of the bouncing jets by varying the jet diameter, velocity, collision angle, and fluid viscosity, which suggests a scaling relation that captures the transition of colliding jets from bouncing to coalescence. This parameter draws parallels between jet coalescence and droplet splashing (crown-splash), indicating that the transition is governed by a surface instability.

Research on precise control of quantum systems occurs in many laboratories throughout the world, for fundamental research, new measurement techniques, and more recently for quantum information processing. I will briefly describe experiments on quantum state manipulation of atomic ions at the National Institute of Standards and Technology (NIST), which serve as examples of similar work being performed with many other atomic, molecular, optical (AMO) and condensed matter systems across the world. This talk is the “story” of my involvement in these subjects that I presented at the 2012 Nobel Prize ceremonies.