Eric Sembrat's Test Bonanza

Supermassive black holes are amazingly exotic and yet ubiquitous objects, residing in the centers of essentially all stellar bulges in galaxies. Recent years have seen remarkable advances in our understanding of how these black holes form and grow over cosmic time, and how energy released by active galactic nuclei (AGN) connects the growth of black holes to their host galaxies and large-scale structures. I will review some recent work that explores these connections, with a focus on statistical studies of AGN clustering and the links between black hole growth and and star formation. I will highlight some new insights into how and when AGN "feedback" is important for galaxy evolution, and discuss some prospects for exciting future progress.

PLEASE NOTE: This is a WEBINAR

Loose sand particles can jam together to become a solid. Think of the dry sand on the beach: it supports your weight so you can walk on it – you don't need to swim in sand. Jammed sand indeed so much resists deformation that it even expands when you try to make it flow. This was already discovered by Osborne Reynolds in 1885. In fact, you can make sand particles jam by making them flow in a container that cannot expand. This effect is known as shear jamming and was discovered only recently. We have now studied the remarkable mechanics of these solid, shear-jammed structures. We did this in a model system, composed out of plastic disks. With an inventive new experimental setup, we were able to perform uniform
shear to a two-dimensional assembly of these disks in a container that does not expand. Deforming the collection of disks from a loose state with no forces between the disks, this model sand developed fascinating force structure. The plastic disks are optically sensitive to the forces acting on them, so these forces could be visualized as fringe patterns. With so much detail about the microscopic contacts in hand, we could for the first time fully establish and also quantify the existence of non-linear mechanical behavior of these shear jammed solids. Moreover, even though particles in these shear jammed packings hardly had the space to move, we uncovered completely unexpected dynamics in the force networks as shown in the image,
when they exposed the packing to repeated deformations. These results provide new perspective and important benchmarks for theoretical modeling of these shear jammed solids. And that's good, because at some point engineers may use the concept of shear jamming to build your new house. Perhaps even better is that it also shows the surprise and beauty in materials as common as sand on the beach.

PLEASE NOTE: This is a WEBINAR

The interplay of shearing and rotational forces in fluids  significantly affects the transport properties of turbulent fluids  such as the heat flux in rotating convection and the angular momentum  flux in a fluid annulus between differentially rotating cylinders. A  numerical investigation was undertaken to study the role of these  forces using plane Couette flow subject to rotation about an axis  perpendicular to both wall-normal and streamwise directions. Using a  set of progressively increasing Reynolds numbers (650 <= Re <= 5200),  our primary findings show the momentum transport for a given Re is a  smooth but non-monotonic function of inverse Rossby number (1/Ro). For  lower turbulent Reynolds numbers, Re <= 1300, a peak in momentum  
transport occurs at 1/Ro=0.2; this peak is 50% higher than the  non-rotating (1/Ro=0) flux and is attributed to the turbulent Taylor  vortices. However, as the shear is increased to Re=5200, a second  stronger peak emerges at 1/Ro=0.03. The flux at the second peak is  nearly 20% larger than the non-rotating flux compared to the Taylor  vortex peak which is now only 16% larger. This finding contributes to  the understanding of the torque maximum found in the high-turbulence  Taylor-Couette experiments in Maryland, USA and Twente, NL.

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Low-luminosity GRBs or X-ray flashes (XRFs), which often accompany supernovae, are typically ascribed to either the supernova shock breakout or weak GRBs powered by the central engine of stellar mass. We propose the tidal disruption of a white dwarf (WD) by an intermediate-mass black hole (IMBH) as another channel for XRFs. Such disruptions last for 100-5000 seconds.  The release of gravitational energy over short time generates a powerful flare. The magnetic field is quickly amplified in the fallback material, and then the BH launches a slow uncollimated jet. The emission from jet photosphere dominates X-rays with Comptonized thermal spectrum, while the expanding jet shell produces most of IR/optical. The prompt flare may be followed by an underluminous fast supernova, resulting from a tidal compression and thermonuclear ignition of a WD. High event rate in dwarf galaxies warrants searches among the known and future transients observed with Swift satellite.

We perform detailed dynamical and spectral modeling of a candidate disruption source GRB060218/SN2006aj. The BH mass is independently estimated to be 20,000 solar masses based on (1) the event duration, (2) the jet base radius from the thermal X-ray component, and (3) the properties of a host galaxy. The supernova position is consistent with a center of a dwarf host galaxy. Other potential candidates are the flashes with very weak/absent supernovae such as XRF040701."

A great part of physics deals with motion, and the essence of sports is the human body in motion.  The components of the human body that produce motion, namely the skeletal muscles and bones, and the sports equipment itself are bound by the laws of physics.  Aspects of various sports, including baseball, basketball, karate, figure skating, golf, tennis, long jump, and more, will be examined using introductory-level physics.  We will also discuss whether we have reached our limits in human performance in certain sports.  All who appreciate the workings of the human body and the laws of science dictating performance in sports are welcome.

Biosketch:
Cüneyt Can is a professor of physics at Middle East Technical University (METU), in Ankara, Turkey, which is internationally accredited and the leading state university.  After completing his undergraduate studies at METU, Dr. Can earned his Master's and PhD degrees from Kansas State University in atomic physics.  Following post-doctoral work at Texas A&M University, he returned to Turkey and to METU, where he has worked for the past 23 years.  Until the completion of his term in 2012, he held the position of Dean of the Faculty of Arts and Sciences.

Natural populations can suffer catastrophic collapse in response to small changes in environmental conditions, and recovery after such a collapse can be exceedingly difficult. We have used laboratory microbial ecosystems to study early warning signals of impending population collapse. Yeast cooperatively breakdown the sugar sucrose, meaning that below a critical size the population cannot sustain itself. We have demonstrated experimentally that changes in the fluctuations of the population size can serve as an early warning signal that the population is close to collapse. The cooperative nature of yeast growth on sucrose suggests that the population may be susceptible to cheater cells, which do not contribute to the public good and instead merely take advantage of the cooperative cells. We confirm this possibility experimentally and explore how such social parasitism can lead to population extinction.

Superbursts are the most powerful repeating thermonuclear flashes observed from accreting neutron stars. Runaway thermonuclear burning of carbon ignites deep in the star's envelope. Close to the crust, superbursts are sensitive to the ill-understood nuclear physics processes in dense neutron-rich matter. We present the latest numerical simulations of carbon burning. Comparing the tail of the simulated lightcurve to observations constrains the depth of carbon ignition, whereas the start exhibits the signs of a shock caused by detonation. Recently increasing observational evidence points at interaction between X-ray bursts and the accretion disk. As the most powerful X-ray bursts, superbursts are important for constraining this interaction. We discuss superexpansion and recent superbursts in transient sources.

Manipulating the texture of foods is central to cooking.  One common manipulation is to induce a phase transition, for example, from a solid to a liquid state, which can occur both during cooking and eating.  In understanding the phase behavior of food materials, we will consider the protein, carbohydrate, and fat molecules that are components of foods that we eat.  Interestingly, these same molecules can also impart unique physical properties to plants and animals, which are critical in biology and physiology.  For example, protein molecules can form structures that provide structural stability for gels such as Jello-O, as well as individual cells in our bodies.   By manipulating molecules in creative ways, chefs and curious cooks can finely tune food texture, and generate innovative cuisine.

PLEASE NOTE: This is a WEBINAR

Two topics in pattern formation for reaction-diffusion equations will be addressed in this talk.  In the first, I will discuss the existence proof for stationary localized spots in the planar and the three-dimensional Swift--Hohenberg equation using geometric blow-up techniques. The spots have a much larger amplitude than that expected from a formal scaling in the far field. One advantage of the geometric blow-up methods is that the anticipated amplitude scaling does not enter as an assumption into the analysis but emerges during the construction.  In the second half, invasive waves are found in a variant of a reaction-diffusion system used to extend an evolutionary adversarial game into space wherein the influence of various strategies is allowed to diffuse.  The original game was derived to model the transition of a war-torn or crime-dominated society towards a peaceful and cooperative society.  The waves are driven by a nonlinear instability that enables an unstable state to travel through an initially uncooperative state and mediate the transition to a cooperative state.  The wave speed's dependence on the various diffusion parameters is also examined.