לוח שנה משולב

In the past few years new classes of supernovae have been discovered that are both brighter and fainter than previously thought possible. The superluminous supernovae have luminosities 100 times greater than a core-collapse supernova, and their origin is a mystery. I will present data on two of the most distant and best-observed events from the Supernova Legacy Survey, and the first radiative transfer model that gives insight into their origin. They seem to result from the creation and spin-down of a magnetar. I'll also discuss a range of both normal and exotic supernovae from the local universe, including an even newer class of superluminous supernovae, and show how new observations are revealing or limiting SN progenitors for the first time. The Las Cumbres Observatory Global Telescope Network (LCOGT) is one of the latest tools allowing new kinds of observations with its 11 node network of one and two meter robotic telescopes spanning the globe. We have now begun the LCOGTSupernova Key Project, which will collect the largest sample of low-redshift supernovae ever obtained: lightcurves and spectroscopy on 450 supernovae over 3 years for use in cosmology, understanding explosions, and determining supernova progenitors.

I will discuss the applicability of atomic clocks to test general relativity and alternative theories of gravity for planned missions such as the Gravitational Redshift Explorer (GRESE). We assume that the spacecraft that orbits the Earth is tracked using the observed tick rate of its clock, which is then compared to the tick rate of a local clock on the ground. The spacecraft's reconstructed 4-D trajectory can reveal the nature of gravitational perturbations in the gravitational field of the Earth testing multiple relativistic effects such as frame dragging and shapiro time delay, and potentially differentiating between different theories of gravity via Parametrized Post-Newtonian Parameters (PPN). On the ground, clocks along with the most recent optical fiber technology measure ground uplift at a precision that competes with existent technology (e.g, GPS, gravimeters). This monitoring has a plethora of applications, which include closer monitoring of the solid Earth tide in areas where hydraulic fracturing is performed, and potentially better monitoring of areas with high seismic and volcanic activity.

A sheet of paper that has been crumpled and flattened retains some amount of shapability that a bare, uncrumpled, sheet does not have: when deformed by external forces, it retains the deformed shape after the forces are removed. Using a frustrated two dimensional lattice of springs, we show that such shapability can be attained in a non-dissipative system. Numerical investigations suggest an extensive number of bistable energy minima using several variants of this scheme. The numerical sheet can be bent into a nearly-closed cylinder that holds its shape. We verify that the deformed shape is locally stable and compare its bending modulus in the deformed state with that in the initial flat state. We investigate the threshold for non-elastic deformation using various kinds of forcing.

Evolution acts on individual variation. Complex biological systems, such as colonies of social insects, are aggregates of multiple agents working together towards collective, higher-order goals, producing emergent collective properties on which natural selection acts. There is no central control dictating the activities of members in the assembly. Instead, agents use local signals that determine their behavior and are received through an intricate interaction network resulting in collective phenotypes. I examine how individual variation among workers in harvester ant colonies affects the collective behavior of the colony, producing individual variation among colonies. I will present work on how the structure of the interaction network among ant workers affects the foraging regulation of colonies of the red harvester ant, Pogonmyrmex barbatus. In addition, I will discuss the causes and consequences of individual variation in the collective behavior of colonies of the black harvester ant, Messor andrei. In both cases, variation at small local scales translates into variation at the system level, creating a behaviorally diverse population.