Eric Sembrat's Test Bonanza

Homotopy method is being used to explore nonlinear partial differential equation system arising from engineering and physics. This new approach is used to compute multiple solutions of nonlinear PDEs and yields the discretized polynomial systems, which involve thousands of variables. This method can also handle the singularities. This talk will cover the recent progress on nonlinear PDEs such as free boundary problem and hyperbolic conservation law problem.

We present a series of experiments demonstrating how animals stay dry.  These adaptations are necessary for survival in rain and other wet environments.  During flash floods, fire ants weave hydrophobic rafts with their own bodies in order to keep their colonies dry.  We discuss their method of self-assembly and present a model that predicts their construction rate.  To survive raindrop impacts, flying mosquitoes take advantage of their low mass, which prevents drops from splashing upon impact.  The resulting force applied is 100-300 gravities, quite possibly the largest survivable force in the natural world.  Animals much larger than insects employ active mechanisms to shed water.  Mammals across four magnitudes in mass can shake off 70% of the water on their bodies in fractions of a second.  We show that wet mammals shake at tuned frequencies to dry and present a scaling law relating animal size and frequencies required to dry.  In this talk, the audience will learn the basics of modeling and experimentation with surface-tension phenomena.

A novel thermal scanning probe lithography (tSPL) method based on the local removal of organic resist materials has been developed at the IBM Research Laboratory in Zurich [1-3]. A polymeric polyphthalaldehyde resist [2-4] responds to the presence of a hot tip by local material decomposition and desorption. Thereby arbitrarily shaped patterns can be written in the organic films in the form of a topographic relief, constrained only by the shape of the tip. The combination of the fast ‘direct development’ patterning of a polymer resist and the in-situ metrology capability of the AFM setup allows to reduce the typical turnaround time for nano-lithography to minutes.

Patterning rates of 500 kHz have been achieved. For this, the mechanics and drive waveform of the scan stage were optimized, achieving high speed linear scanning with an overall position accuracy of ± 10 nm over scan-ranges and scan-speeds of up to 50 μm and 20 mm/s, respectively. A pre-tension-and-release strategy was used to actuate the cantilever above its resonance frequency of 150 kHz. Fabrication of three dimensional patterns is done in a single patterning step by controlling the amount of material removal at each pixel position. The individual depths of the pixels are controlled by the force acting on the cantilever.

The structuring capability in the third dimension adds an entirely new feature to the lithography landscape and finds applications e. g. in multi-level data storage, nano/microoptic components and directed positioning of nanoparticles. For the latter, shapematching guiding structures for the assembly of nanorods of size 80nm × 25nm have been written by thermal scanning probe lithography [4]. The nanorods were assembled into the guiding structures by means of capillary interactions. Following particle assembly, the polymer was removed cleanly by thermal decomposition and the nanorods are transferred to the underlying substrate without change of lateral position. As a result we demonstrate both the placement and orientation of nanorods with an overall positioning accuracy of ≈ 10 nm onto an unstructured target substrate.

[1] D. Pires, J. L. Hedrick, A. De Silva, J. Frommer, B. Gotsmann, H. Wolf, M. Despont,

U. Duerig, and A. W. Knoll, Science 328, 732 (2010).

[2] A. W. Knoll, D. Pires, O. Coulembier, P. Dubois, J. L. Hedrick, J. Frommer, U.

Duerig, Adv. Mat. 22, 3361 (2010).

[3] P. C. Paul, A.W. Knoll, F. Holzner, M. Despont and U. Duerig, Nanotechnology 22,

275306 (2011).

[4] F. Holzner, C. Kuemin, P. Paul, J. L. Hedrick, H. Wolf, N. D. Spencer, U. Duerig,

and A. W. Knoll, NanoLetters, 11, 3957 (2011).

I will summarize our current understanding on the relation between the evolution of black holes and galaxies in the local universe. I will show that the growth of supermassive black holes as traced by optically luminous active galactic nuclei is strongly linked to the on-going formation of stars in the bulge component of galaxies. It is likely that this co-evolution is driven by the accretion and radial transport of cold gas, but major mergers of galaxies are not the primary mechanism for doing this. I will show that the fuel source for the black hole growth may be mass loss from intermediate mass stars and that the black hole growth may be limited in part by feedback from supernovae. I will also show that the characteristic mass scales for the populations of growing black holes and bulges are substantially lower now than in the past. The most massive black holes are largely quiescent today with low-level activity driven by the slow accretion of hot gas. The weak radio jets such black holes commonly produce may nonetheless may play a key role in suppressing star formation, keeping their surrounding host galaxy "red and dead".

The statistics of newly discovered z>~6 galaxies---their abundance and clustering---have allowed us to study their ensemble properties, but the difficulties inherent in detecting, resolving, and obtaining spectra of these distant, faint objects has prevented a deeper empirical exploration of their internal physics. However, in advance of observatories like GMT and TMT, multi-wavelength observations can be a useful probe of the high-redshift ISM. I will present a novel analytic model for the internal physics of z>~6 galaxies that, when combined with information from galaxy statistics, probes an enormous range of distance scales---from the tens of megaparsec regions over which cosmic variance operates to the tens of parsec-sized photo-dissociative regions within giant molecular clouds---a range that makes investigations difficult with numerical simulations. I will apply this model to understanding the X-ray emission from faint AGN and to predicting future observations of CO emission lines with ALMA.

Gamma-ray bursts (GRBs) have been shown by the Fermi LAT to be a source of gamma rays with energies as high as ~100 GeV in the rest frame. Detection at higher energies may be possible with next-generation ground-based instruments. I will present results from a new simulation of GRB detections with the upcoming Cherenkov Telescope Array (CTA), using models based on the combined observations of Fermi LAT and lower-energy satellite experiments. This simulation allows the prediction of the overall detection rate, how this rate might vary as a function of telescope performance and uncertain GRB statistical properties, and the likely properties of detected GRBs. I will also show a preliminary calculation of the GRB detection rate with the HAWC (High-Altitude Water Cherenkov) observatory using a similar model. Finally, I will end with a brief mention of how new GRB detections in the GeV band could help improve our understanding of UV-optical radiation fields in the universe.

As experiments probe quantum phenomena ever more deeply, it becomes difficult to believe that there is anything other than pure, unitary, quantum time evolution. Without wave-function collapse, the physicist is left with the many-worlds interpretation as the source of quantum indeterminism. (I say "physicist" because I can't defend against all philosophical contortions.)

However, if one is willing to take a radical view of statistical mechanics, it is possible to have only unitary time evolution, and still have a single "world." I will explain just what that radical departure is and how one achieves quantum determinism. A basic assumption/explanation with be "special" microscopic states. Finally, I will describe an experimental test of these ideas that is well within the realm of feasibility.

X-ROS signaling is a novel redox signaling pathway that links mechanical stress to changes in [Ca2+]i.  This pathway is activated rapidly and locally within a muscle cell under physiological conditions, but can also contribute to Ca2+-dependent arrhythmia in heart and to the dystrophic phenotype in heart and skeletal muscle 1, 2.  Upon physiologic cellular stretch, microtubules serve as mechanotransducers to activate NADPH oxidase 2 (NOX2) in the transverse tubules and sarcolemmal membranes to produce reactive oxygen species (ROS).  In heart, the ROS acts locally to activate ryanodine receptor Ca2+ release channels in the junctional sarcoplasmic reticulum, increasing the Ca2+ spark rate and "tuning" excitation-contraction coupling.  In skeletal muscle, where Ca2+ sparks are not normally observed, the X-ROS signaling process is muted.  However in muscular dystrophies, such as Duchenne Muscular Dystrophy and dysferlinopathy, X-ROS signaling operates at a high level and contributes to myopathy.  Importantly, in skeletal muscle Ca2+ permeable stretch-activated channels are activated by X-ROS and contribute to the cellular pathology.  In brief, X-ROS provides an exciting new mechanism for the mechanical control of redox and Ca2+ signaling in cardiac and skeletal muscle.

1. Khairallah RJ, Shi G, Sbrana F, Prosser BL, Borroto C, Mazaitis MJ, Hoffman EP, Mahurkar A, Sachs F, Sun Y, Chen YW, Raiteri R, Lederer WJ, Dorsey SG, Ward CW. Microtubules underlie dysfunction in duchenne muscular dystrophy. Sci Signal. 2012;5:ra56

2. Prosser BL, Ward CW, Lederer WJ. X-ros signaling: Rapid mechano-chemo transduction in heart. Science. 2011;333:1440-1445

Activation of T lymphocytes by antigen-presenting cells involves cell spreading driven by large-scale physical rearrangements of the actin cytoskeleton and the cell membrane, and accompanied by the assembly of signaling molecules into dynamic microclusters. Several recent observations suggest that mechanical forces are important for efficient T cell activation. How forces arise from the dynamics of the cytoskeleton and the membrane during contact formation, and their effect on microcluster assembly and signaling activation is not well understood. We imaged the membrane topography, actin dynamics and the spatiotemporal localization of signaling clusters during the very early stages of spreading. We found that the formation of signaling clusters was closely correlated with the movement and topography of the membrane in contact with the activating surface. Further, we observed membrane waves driven by actin polymerization originating at these signaling clusters. These actin-driven membrane protrusions likely play an important role in force generation at the immune synapse. In order to study the role of cytoskeletal forces during T-cell activation, we studied cell spreading on elastic substrates to measure cellular forces during spreading. We found that substrate stiffness influences cell morphology, actin dynamics and cellular traction forces. Efforts to determine the quantitative relationships between cellular forces and signaling are underway. Our results suggest a role for cytoskeleton driven forces during signaling activation in lymphocytes.

Studies that involve single vortex dynamics, vortex-vortex interactions, and vortex-impurity interactions are essential in developing a deeper understanding of the nature of superfluidity and in particular, superfluid turbulence.  In highly oblate systems, vortex dynamics have a two-dimensional (2D) nature and the resulting superfluid characteristics may be substantially different from those in three-dimensional (3D) superfluids. However, there have been remarkably few experimental studies of 2D vortex dynamics in superfluids. Therefore, to study 2D vortex dynamics and interactions, it is necessary to first develop experimental methods that can generate vortices and vortex distributions in nominally 2D systems,
such as highly oblate Bose-Einstein condensates (BECs).

Several experimental methods that were developed to generate or manipulate quantized vortices in highly oblate dilute-gas BECs will be presented in this seminar.  Two of these experiments generate multiple singly quantized vortices in a relatively stochastic manner leading to disordered vortex distributions. From these two vortex methods, the physics of high vorticity and highly disordered systems may be observed and studied in a highly oblate system. These methods may prove useful in studies of 2D quantum turbulence. The other two experiments involve newly developed techniques for controlled generation and manipulation of vortices. One of these methods creates multiply quantized pinned vortices with a certain degree of control in the generated vorticity. The other method reliably creates a pair of singly quantized vortices of opposite circulation, whose positions can be easily manipulated after creation, such that they can be placed in any location within the BEC. The two techniques may be scalable to higher number of vortices and may prove useful in superfluid dynamics and vortex interactions that require repeatable vortex distributions. Taken together, these tools and methods may be applicable to many further studies of vortex physics in highly oblate BECs.