Past Events

  • Condensed Matter Seminar: "The physical chemistry of natural selection: How can we explain the high yields and high rates of biochemical reactions?"

    David Rittenhouse Laboratory, A4

    Jean-Louis Sikorav (Ministère de l'Economie et des Finances)

    The goal of this seminar is to present the main findings of an ongoing inquiry of the foundations of biology (1). The purpose of this investigation is to describe the elements, the logic and the principles of biology, and to construct biological theories using the language and the methods employed in other disciplines. This work brings to the fore the existence of a unity of knowledge, also revealed through the study of the science of research shared by all disciplines (2).

  • Condensed Matter Seminar: "Long Term 3D Imaging by FIBSEM for Neurons and Cell Biology and Correlation to Cryo Fluorescence Microscopy"

    David Rittenhouse Laboratory, A4

    Harald Hess (Howard Hughes Medical Institute, Janelia Research Campus)

    3D Electron microscopy volume data can be acquired by a variety of approaches.  Focused Ion beam – scanning electron microscopy, FIBSEM, offers no limitation on section thickness, so that isotropic voxels with 8 nm or less sampling in x,y,z dimensions can be acquired.  This capability opens a new regime where entire cells can be imaged with 4 nm voxel sampling, thereby surpassing partial cell or section limitations to complete cell data.

  • Condensed Matter Seminar: "Wisdom of hives and mounds: collective problem solving by super-organisms"

    David Rittenhouse Laboratory, A4

    Lakshminarayanan Mahadevan (Harvard University)

    Social insects are capable of solving complex physiological problems using collective strategies. I will discuss our work on some of these problems  that include the physiology and morphogenesis of termite mounds, and  active mechanisms for ventilation, mechanical adaptation and  thermoregulation  in bee aggregates.

  • Condensed Matter Seminar: "Ideas on magma motion within the lithosphere: percolation, channelization, and stress-driven segregation"

    David Rittenhouse Laboratory, A4

    Mousumi Roy (University of New Mexico)

    Although we know that magma is generated by partial melting of rocks at depth, we have less of an understanding of the processes that transport magma from great depths (>100-150 km) into the shallower (20-0 km) crustal plumbing systems of volcanic zones.   I shall discuss how interstitial melt migrates via percolative flow, and ideas on how it eventually becomes focused and reorganized into networks.  Field and geochemical observations suggest that these networks are characterized by thermal and chemical disequilibrium between the magma and surrounding rock.  I

  • Condensed Matter Seminar: "Geometry and mechanics of feet and fins"

    David Rittenhouse Laboratory, A4

    Mahesh M. Bandi (Okinawa Institute of Science and Technology Graduate University)

    The stiffness of propulsive appendages, such as feet and fins, is important in locomotory function. In this talk, I show that curvature-induced stiffness is the common principle underlying the stiffness of both primate feet and rayed fish fins. We use mathematical models, physical models, and biological experiments to arrive at this conclusion. The principle is evident in a drooping dollar bill that significantly stiffens upon slightly curling it in the transverse direction.

  • Condensed Matter Seminar: "Structure and Topology of Band Structures in the 1651 Magnetic Space Groups"

    David Rittenhouse Laboratory, A4

    Ashvin Vishwanath (Harvard University)

    We describe a powerful theoretical approach to studying electronic band structures, which associates them with elements of a vector space. The set of consistent band structures in a space group can then be expanded in terms of a small set of basis vectors. We calculate the dimension of this vector space, and the necessary electron fillings to obtain band insulators in all magnetic space groups.

  • Condensed Matter Seminar: "Enhanced optical and magnetic microscopy by orientation-dependent modulation of single-molecule and nitrogen-vacancy-center emission"

    David Rittenhouse Laboratory, A4

    Mikael Backlund (Harvard University)

    Selection rules impose geometrical constraints on the interactions of light and matter. In
    particular, an emitter with a well-defined orientation will emit photons of a characteristic
    polarization and wavevector distribution, even as viewed in the far field. Knowledge of these
    distributions can be leveraged to enhance a number of state-of-the-art microscopy techniques. In
    the first part of the talk I will discuss such an approach to single-molecule localization
    microscopy, relevant for single-molecule tracking and super-resolution imaging. It is known that

  • Condensed Matter Seminar: "Controlling Strong Light Matter Coupling with Photonic Crystals"

    David Rittenhouse Laboratory, A4

    Hui Deng (University of Michigan)

    Microcavity exciton-polaritons provide a unique photonic platform that manifests non-equilibrium quantum orders. It combines strong nonlinearity and rich many-body physics of matter with robust coherence and ready accessibility of light, allowing diverse quantum phenomena at high temperature, on a photonic chip. To go beyond 2D condensation physics, it becomes important to control the fundamental properties of polaritons without destroying the quantum orders.

  • Condensed Matter Seminar: "Soft matter physics in the gut"

    David Rittenhouse Laboratory, A4

    Sujit S. Datta (Princeton University)

    The gut governs digestion and nutrient absorption, is a promising target for drug delivery, and teems with micro-organisms that can have remarkably strong effects on host health. Despite its importance, however, little is known about how the structure and function of the gut are influenced by many of the soft materials that transit through it regularly.

  • Condensed Matter Seminar: "Mechanical Cell Biology of Microbes"

    David Rittenhouse Laboratory, A4

    Enrique Rojas (Stanford University)

    Research in microbial physiology has traditionally focused on understanding biochemical pathways and, more recently, on elucidating the surprisingly complex structure of microbial cytoplasm.  On the other hand, the whether mechanical forces also play a role in controlling sub-cellular processes in microbes has been overlooked. I will highlight several novel paradigms by which microbes use mechanical (and electrical) factors as signals to control cell growth, division, and survival, and highlight how the remarkable mechanical properties of the cells are critical for these p