Condensed Matter & Biological Physics Seminar Condensed Matter & Biological Physics Seminar| Date | Speaker | Affiliation | Title | Host |
|---|---|---|---|---|
| September 4th | Benny Davidovitch | University of Massachusetts | Instabilities and morphological phases of stressed elastic membranes | Marchetti |
Crumpled papers, wrinkled skins, and buckled plant leaves are few familiar examples of the rich variety of patterns that elastic membranes may exhibit under quite featureless constraints. One may ask: Does a morphological "phase space" exist, according to which the many possible membrane patterns are classified? What are the relevant parameters that determine whether a distribution of forces and constraints gives rise to a smooth shape (e.g. periodic wrinkles) or to an irregular one, characterized by localized ridges and vertices (e.g. crumpled sheets). In this talk I will address these questions, by focusing on an elementary case: highly-symmetric membrane (homogenous, isotropic, of rectangular shape) that is buckled under uniaxial compression and is subjected to a uniform tension in the orthogonal direction. I will show that a surprisingly rich "phase diagram" of distinct morphologies is spanned by a pair of dimensionless parameters that encapsulate the relevant mechanical conditions and geometric constraints. In particular, a novel series of "period fissioning" instabilities gives rise to a smooth wrinkling cascade when the tension is sufficiently large. This instability mechanism is shown to underlie a recently-discovered phenomenon: A smooth cascade of wrinkles, in uniaxialy-compressed ultrathin membranes, floating on liquid and subject to tension and geometric frustration due to strong capillary forces. |
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| September 11th | Xavier Illa | Department of Physics, Syracuse University | CREEP FRACTURE: EXPERIMENTS AND SIMULATIONS | Shradha Mishra |
| September 18th | ||||
| September 25th | Jennifer Ross | UMass, Amherst | Building Biological Complexity 1-2-3 | Marchetti |
| Kinesin and cytoplasmic dynein are microtubule-based motor proteins that actively transport material throughout the cell. This transport is vital to maintain communication and motion of materials in the long axons of the nervous system. In particular, lack of cargo transport down the axons leads to neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease. ALS is the disease that afflicts physicist Stephen Hawking. We investigate the innate transport abilities of these motor proteins outside of the cell. We find that dynein has a greater ability to stay bound in the presence of obstacles on the microtubule track. Kinesin, on the other hand, can move robustly, but dissociates when confronted by a blocked path. Dynein's ability to hang on is likely due to its inherent flexibility and ability to move in reverse. | ||||
| October 2th | ||||
| October 9th | Will Oliver | Lincoln Laboratory, Massachusetts Institute of Technology | Amplitude spectroscopy with a superconducting artificial atom | Plourde |
| Superconducting persistent-current qubits are quantum-coherent artificial atoms with multiple energy levels. In the presence of large-amplitude harmonic excitation, the qubit state can be driven through one or more of the energy-level avoided crossings. The resulting Landau-Zener-Stueckelberg (LZS) transitions mediate a rich array of quantum-coherent phenomena as a function of the driving amplitude and frequency. In this talk, we present three demonstrations of LZS-mediated quantum coherence in a strongly-driven niobium persistent-current qubit. The first is Stueckelberg interferometry [1], with which we observed quantum interference fringes in the transition rates for n-photon transitions, with n = 1…50. The second is microwave-induced cooling [2], by which we achieved effective qubit temperatures < 3 mK, a factor 10x-100x lower than the dilution refrigerator ambient temperature. The third is amplitude spectroscopy [3], a spectroscopy approach that monitors the system response to amplitude rather than frequency. This allowed us to probe the energy spectra of our artificial atom from 0.01 – 120 GHz, while driving it at a fixed frequency 0.16 GHz. These experiments exhibit a remarkable agreement with theory, and are extensible to other solid-state qubit modalities. In addition to our interest in these techniques for fundamental studies of quantum coherence in strongly-driven systems, we anticipate they will find application to qubit control and state-preparation methods for quantum information science and technology [4]. | ||||
| October 16th | Maria Kilfoil | McGill University, Department of Physics | Cell Architecture: Soft Matter Physics Meets Biology | Marchetti |
| In this talk, I will present a comprehensive study of biological systems using confocal, fluorescence, and light microscopy combined with particle tracking image analysis and microfluidics. I will present novel quantitative and automated morphometric measurements my group has developed and implemented in budding yeast, a prototypical cell model system for studying cell division. We use this system to study the effect of perturbation of the mitotic kinesin motor proteins on spindle dynamics and on cell volume homeostasis. In the second part, I will show preliminary investigations of the response of the mechanosensitive channel MscL to osmotic stress in living E. coli bacteria. For these experiments, a micro-fluidic device was developed to determine cell viability over multiple generations following exposure to static or temporally varying stress stimuli, correlated with cellular levels of EGFP-tagged MscL. In the third part, I will present the first microscopic rheology studies of microtubule solutions and actin and microtubule composites, and show network findings regarding network compressibility that challenge theoretical explanation. | ||||
| October 23th |
Dennis Discher (joint with BMCE seminar) |
Biophysical Eng. and Nanobiopolymer Lab, University of Pennsylvania | Evading Clearance to enhance Nano-Delivery: Surprises in Shape and Exploitation of a 'Marker of Self' ligand | Forstner |
| Evading Clearance to enhance Nano-Delivery: Surprises in Shape and Exploitation of a 'Marker of Self' ligand” Shape effects of drug delivery vehicles are largely unexplored, especially in vivo, but we have recently shown that flexible cylinders circulate in vivo longer than spheres of identical composition (1). Flexible filomicelles increase both dosage and tumor-selective effects in vivo relative to spheres and thus appear promising as anticancer drug delivery systems. However, any particle injected or surface implanted in us or any other mammal must contend with Macrophages that have – for eons – swept up invading bacteria, yeast, viruses, and other pathogens. At the same time, Macrophages leave our own ‘Self’ cells alone. The Foreign vs Self difference certainly does not reside in steric repulsion by the glycocalyx, which some have argued is well-mimicked by the polymer PEG. We have sought to address how Macrophages specifically recognize Self and to define its physicochemical limits, and – based on limited data from mouse – we have focused on the cell-surface protein CD47 found on all of our own cells. We demonstrate a two-step procedure for recognizing intruders that helps avoid misdirected attacks. In the first step, which is well known, Macrophages adhere and begin engulfing objects studded with antibodies or plasma complement proteins that bind interlopers and will also bind to the body’s own cells. But before a macrophage engulfs its target, it also checks for the second form of identification on all self cells, CD47. The ~100 aa extracellular domain of CD47 proves sufficient to induce a macrophage to disengage a cell from the same species or even a synthetic particle decorated with this domain (2). We detail the divergence in Foreign vs Self adhesive signaling mechanisms, the dependence on protein densities, and the particle size dependence for this fundamental facet of immunocompatability. | ||||
| October 30th | ||||
| November 6th | Eun-Ah Kim | Cornell University Ithaca | Topological quantum phase transitions | Jennifer Schwarz |
| Characterizing and detecting topological order is one of the central questions in the field of topological phases. The challenge lies in that these new type of quantum ground states are not associated with any local broken symmetry. Of broader interest in the context of quantum phase transitions(QPT) is a question of the nature of a quantum critical point when a system enters a topologically ordered phase. In this talk I will discuss our recent progress in describing a topological phase transition between an Abelian and a non-Abelian topological phase and in characterizing conformal quantum critical point. | ||||
| November 13th | Valerica Raicu | Department of Physics, University of Wisconsin | Determination of structure and distribution of protein complexes in living cells | Liviu Movileanu |
| When an optically excited molecule, called a 'donor,' comes in close proximity (< 10 nanometer) of an unexcited one, part of the energy may be transferred to the second molecule (called an 'acceptor'). This effect, known as Förster (or Fluorescence) Resonance Energy Transfer (FRET), causes the acceptor molecule to emit light with red-shifted wavelengths compared to the excitation wavelength. Detection of such spectral shifts helps determine whether two fluorescent molecules interact with one another. When donor and acceptor tags are fused to proteins of interest (which may be non-fluorescent), FRET may be used to probe whether the tagged proteins form functional complexes in living cells. This talk will present recent advances that led to the development of FRET into a method for determination of structure and localization in living cells of protein complexes. I will begin by identifying the main requirements that any quantitative FRET technology for in vivo investigations should meet. These requirements will be discussed in the broader context of information extraction from fluorescence images of molecular distributions undergoing continuous changes due to diffusion. Then, I will introduce our FRET method, which relies on a spectrally resolved two-photon microscope and a simple theory of FRET in molecular complexes to determine the size and geometry of protein complexes in living cells. I will conclude the talk with an overview of the results obtained from our recent studies of oligomeric complexes of some membrane receptors in living cells. | ||||
| November 20th | Erik Luijten | Northwestern | Complex fluids with dipolar interactions: Phase behavior, self-assembly, and hydrodynamics | Bowick |
| December 4th | Kurt Jacobs | Department of Physics, University of Massachusetts Boston | Creating Cat-States in Nanoresonators Using Continuous Measurement | LaHaye Matthew |
| I'll will discuss how a nanoresonator can be prepared in mesoscopic superposition states merely by monitoring a qubit coupled to the square of the resonator.s position. This works for thermal initial states, and does not require a third-order nonlinearity. The required coupling can be generated using an open-loop control protocol or a perturbative coupling. I will present simulations of the complete preparation process, including environmental noise. The talk is based on PRL 102, 057208 (2009). | ||||
| Wed. December 9th (Different day) | Silke Henkes | TBA | Jennifer Schwarz | |
| December 10th | NYCMworkshop | |||
| December 11th | Jean-Savin Heron | l’Institute Néel and Universite Joseph Fourier in Grenoble, France | TBA | Matthew LaHaye |
| Date | Speaker | Affiliation | Title | Host |
|---|---|---|---|---|
| January 22nd | ||||
| January 29th | ||||
| February 5th | ||||
| Tuesday February 9th (4:00 pm) different day and time | Michael Lawler | Binghamton University | Marchetti | |
| February 19th | ||||
| February 26th | ||||
| March 5th | ||||
| March 12th | Spring Break | |||
| March 19th | ||||
| March 16th | ||||
| April 2nd | ||||
| April 9th | Tatyana Svitkina | University of Pennsylvania | TBA | Jennifer |
| April 16th | Prof. Michael Brenner | Harvard | TBA | Bowick |
| April 23rd | ||||
| April 30rd | ||||
| Jan 22 | ||||