Past Events

  • Department Colloquium: "Challenges for Cosmology on Galaxy Scales"

    David Rittenhouse Laboratory, A8

    Benoit Famaey (Strasbourg Observatory)

    While there is indisputable observational evidence for a new degree of freedom behaving as a collisionless fluid of particles on large scales, i.e. dark matter, there is no such solid evidence on galaxy scales. On the contrary, the current standard model of cosmology is plagued with numerous challenges at these scales, which we review here.

  • Math-Bio seminar: "Local Shape from Shading with a Generic Constraint"

    Carolyn Lynch Laboratory, room 318

    Benjamin Kunsberg, Brown University

    Humans have a remarkable ability to infer shape from shading (SFS) information. In computer vision this is often formulated with a Lambertian reflectance function, but it remains under-posed and incompletely solved.  Abstractly, the intensity in an image is a single valued function and the goal is to uncover the vector valued normal function. This ill-posedness has resulted in many proposed techniques that are either regularizations or propagations from known values. Our goal is to understand, mathematically and computationally, how we solve this problem.

  • Astro Seminar: "Probing Dark Energy with the Canadian Hydrogen Intensity Mapping Experiment (CHIME)"

    David Rittenhouse Laboratory, A6

    Richard Shaw (University of British Columbia)

    CHIME will use the 21cm emission line of neutral hydrogen to map large-scale structure between redshifts of 0.8 and 2.5. By measuring Baryon Acoustic Oscillations (BAO) we will place constraints on the dark energy equation of state as it begins to dominate the expansion of the Universe, particularly at redshifts poorly probed by current BAO surveys.

  • Professor Gary Gibbons: "Introduction to Supergravity"

    DRL 2C6

    Gary Gibbons, Visiting Distinguished Professor (Cambridge, UK)

    Supergravity is a theory of gravity incorporating a super-symmetry", that is a symmetry between Fermions and Bosons. The boson in question is the graviton which carries spin 2 and its fermionic partner is the gravitino which carries spin 3/2. The first is governed classically by Einstein's equations and the second by the Rarita-Schwinger equations.

  • Math-Bio seminar: "Predicting the evolution of influenza"

    Carolyn Lynch Laboratory, room 318

    Michael Lässig, University of Cologne

    The human flu virus undergoes rapid evolution, which is driven by interactions with its host immune system. We describe the evolutionary dynamics by a fitness model based on two phenotypes of the virus: protein folding stability and susceptibility to human immune response. This model successfully predicts the evolution of influenza one year into the future. Thus, evolutionary analysis transcends its traditional role of reconstructing past history.

  • Thesis Defense: "The Dark Energy Survey Y1 Supernova Search: Survey Strategy Compared To ForcCasts And The Photometric Type IA SN Volumetric Rate

    David Rittenhouse Laboratory, 4E9

    John Fischer (UPENN)

  • Condensed Matter Seminar: "Imposing Curved Shapes on Solid Sheets: Instabilities, Isometries and Asymptotic Isometries"

    David Rittenhouse Laboratory, A4

    Benny Davidovitch (UMass, Amherst)

    Imposing a curved shape on a solid sheet, generates in it elastic stress. This familiar motif is a consequence of Gauss’ theorema

    Egregium, which posits that there exists no isometric map between two surfaces of different Gaussian curvatures. This coupling between geometry (curvature) and mechanics (stress) underlies the morphological richness observed in solid sheets, and their nontrivial response to exerted forces.

  • Astro Seminar: "What Sets the Maximum Rotation Rate of Neutron Stars? "

    DRL A6

    Ira Wasserman (Cornell)

    The fastest rotating neutron star spins at a frequency of 716 Hz, or a period of about 1.4 milliseconds. This rapidly rotating neutron star was discovered about 30 years after the previous record holder, at 642 Hz.  Almost all equations of state of nuclear matter would permit faster rotation rates. Why don't they exist? 

  • NSF GRFP Fellowship Application Workshops for Graduate Students

    *Once you have signed up for a date, you will receive information on the location and what to do to prepare.*

    Kristen Coakley, Assistant Director Science Outreach Initiative (UPenn)

    If you would like to sign up to attend a workshop, please email Kristen Coakley ( with your preferred date.  All workshops cover the same material so no need to attend more than once.

    Spots are limited and will be assigned on a first come first served basis.  Additional workshops may be scheduled if interest warrants it.

    Other dates are as follows:

  • Math-Bio seminar: "Geography and Adaptation

    Carolyn Lynch Laboratory, RM 318

    Peter Ralph (University of Southern California)

    Most species are distributed across geography, and so can develop regional differences in different parts of the range. These may often be as a result of natural selection, and the geographic scale on which different solutions to evolutionary problems can appear -- the spatial resolution of adaptation -- is determined by a balance between migration, selection, and availability of genetic variation.