NYU-CMU Visitors Seminar at UPR-RP

Date: October 19-20

Thursday October 20, 4:30-5:30 pm. Room NCN A-211.

NYU-CMU Visitors Seminar for the Chemistry Department: Architectural Diversity in Hydrogen-bonded Host Frameworks: From Molecular Jaws to Cylinders to Organic Zeolites.

Michael Ward (NYU Department of Chemistry and Head of NYU MRSEC).

Lamellar inclusion compounds synthesized by directed assembly of guanidinium organomonosulfonates (GMS) and disulfonates (GDS) display a variety of framework architectures that are characterized by “zeolite-like” pores bounded by organic walls and a common two-dimensional (2D) network of complementary guanidinium ions (G) and sulfonate moieties (S) assembly through charge-assisted hydrogen bonds. The structural robustness of this network and the versatility of organic synthesis provides an avenue to frameworks with well-defined pores with sizes, shapes and physicochemical characteristics that can be tuned systematically without loss of generic architectural features, representing a rare example of true “crystal engineering.” These pores can be occupied by functional guest molecules with retention of framework architecture, illustrating a materials design strategy wherein function and solid-state structure are regulated independently. The large number of GMS host-guest combinations permits grouping of the inclusion compound architectures according to simple molecular parameters, enabling more reliable structure prediction for this class of compounds than for molecular crystals in general. In more recent developments, these frameworks have been used for the inclusion of laser dyes, with control of aggregation state, construction of “endo-inclusion cavities” through the use of multivalent calixarenes, and a new generation of 3D zeolite-like compounds constructed entirely from hydrogen bonds using design principles based on Archimedean solids.

Thursday October 20, 4:00-5:00 pm. Room NCN C-310.

NYU-CMU Visitors Seminar for the Physics Department: “The Tipping Point:  How Does A Little Noise Make a Big Difference?”

Dan Stein (NYU Dean for Science, and Departments of Physics & Mathematics).

Abstract: Small random fluctuations, either of thermal or quantum origin, are the cause of many important and interesting physical phenomena. These include chemical reactions, nucleation in phase transitions (i.e., the formation of a droplet of one phase within another phase), and the formation of unusual spatially localized states in various condensed matter systems. In all of these, random fluctuations (or `noise'), no matter how small, eventually drives a physical system from one stable state to another.

We consider both classical and quantum noise. In classical field theories, a crossover between different activation behaviors occurs as one or more control parameters are varied.  This crossover has some (but not all) features of a second-order phase transition. This transition shares a number of features with the well-known crossover from thermally activated hopping to quantum tunneling through a barrier as temperature is lowered in certain quantum field theories.

We also discuss two timely applications from mesoscopic physics: thermally induced breakup of monovalent metallic nanowires, and stochastic reversal of magnetization in thin ferromagnetic annuli. Each are of interest both from the point of view of fundamental physics and for potential technological applications, some of which will be discussed.


Thursday October 20, 4:00-5:00 pm.

NYU-CMU Visitors Seminar for the Mathematics Department: Room NCN A-211

Title: Singular Perturbation Models in Phase Transitions. Giovanni Leoni (Department of Mathematics and Associate Director of the Center for Nonlinear Analysis)

In this talk we describe some recent results on variational models proposed in the physics literature to describe the onset of pattern formation.

Plane-like minimizers in periodic media. Tim Blass (Postdoctoral Fellow in Mathematics at CMU)

Abstract: This presentation will describe methods for constructing plane-like minimizers of periodic energy functionals via gradient descent and perturbation methods. These minimizers are used to compute the associated minimal average energy, which as a physical interpretation in terms of crystal shape.