Colloquia & Seminars
  • LPS Seminar
    Speaker Name: Dr. Miao Yu

    Speaker Institution : Dept. of Mechanical Enginneering, UMCP

    Title : Transforming acoustic sensing: from bio-inspiration to application of advanced materials

    Abstract : Acoustic sensors play an important role in many areas, such as safety (e.g., sonar arrays), public health (e.g., ultrasonic imaging), surveillance (e.g., underwater communication and navigation), and industry (e.g., non-destructive damage detection). However, conventional acoustic sensors inevitably suffer from some fundamental limitations, which hinder the performance of current acoustic technologies. In this talk, various efforts on the development of acoustic sensors that can potentially overcome these limitations at the Sensors and Actuators Laboratory (SAL) of the University of Maryland will be discussed. First, we will discuss how learning from nature can help overcome the fundamental size constraint of directional acoustic sensors. In nature, one striking innovation to overcoming this constraint is found in the parasitic fly Ormia ochracea. The auditory receptors are forcibly set close to each other (500 microns apart) while exhibiting a remarkable ability to localize its host at 5 kHz. We will show how the understanding of the underlying biophysics of fly ear can lead to the development of a micro-scale sensor overcoming a previously-insurmountable size constraint. Second, we will discuss how the application of advanced materials can help greatly enhance the performance of acoustic sensors. Graphene is believed to be one of the strongest materials and the thinnest film in the universe. We will show how the unique mechanical properties can be applied in the development of miniature acoustic pressure sensors for achieving unprecedentedly high sensitivity, large bandwidth, and large dynamic range. Further, we will show how to use acoustic metamaterials to manipulate acoustic waves at subwavelength scales. This enables a sensing paradigm that can help overcome the fundamental detection limit of conventional acoustic pressure sensors.

    Notes: For guests attending the LPS seminar, please use the phone on the left hand side of the front door to call the receptionist for entry. LPS is located at 8050 Greenmead Drive in College Park. There is parking at LPS and overflow parking at the adjacent LTS building but not at the 4H building. LPS is on the UMCP shuttle route; take #105 for the Courtyard Apts.
    When: Wed, March 4, 2015 - 3:30pm
    Where: Lab for Physical Sciences
  • Plasma Physics Seminar
    Speaker Name: Naoki Bessho

    Speaker Institution : NASA Goddard/University of Maryland

    Title : Magnetic reconnection and electron physics: fine structures in electron distribution functions

    Abstract : We investigate magnetic reconnection (antiparallel, symmetric, without guide field) and electron physics by means of two-dimensional particle-in-cell simulations. When collisionless reconnection occurs, an electron-scale thin current layer is formed in the vicinity of an X-line. Around that region is called an electron diffusion region, where electrons are unmagnetized and energy conversion from magnetic energy to kinetic energy occurs. In an electron diffusion region, electrons meander across the magnetic neutral line during acceleration by the reconnection electric field. At the same time, a magnetic field normal to the current sheet turns the electron velocity and a partial gyration occurs. As a result, electron distribution functions show a variety of fine structures in the electron diffusion region: a triangular shape with multiple striations at the X-line, arc and swirling structures in the downstream, and a ring structure near the edge of an electron jet. We traced particle trajectories to identify the origin of those fine structures. Also, we analytically solve the electron motion in the vicinity of the X-line, and obtained formulas for the separation of striations and a triangular shape of an electron distribution function. Based on a Cluster observation of magnetic reconnection in the Earth's magnetotail, we predict the magnitude of the separation of striations and the length of each striation in a momentum space of an electron distribution function near the X-line. Our study will guide identification of electron diffusion regions during reconnection based on satellite measurements, such as NASA's upcoming MMS mission.
    When: Wed, March 4, 2015 - 4:00pm
    Where: ERF 1207, Large Conference Room
  • High Energy Physics Seminar
    Speaker Name: Benjamin Carlson

    Speaker Institution: Carnegie Mellon University/Fermilab

    Title: "Search for Stealth Superwymmetry at the LHC"

    Abstract: Supersymmetry (SUSY) can simultaneously solve the hierarchy problem, allow unification of the fundamental interactions, and provide a candidate for dark matter. Most searches for SUSY focus on the presence of large missing transverse energy (MET) carried away by the lightest SUSY particle. Recent high-MET searches at the CERN LHC have not yet found evidence for SUSY. Therefore, it is important to study well-motivated alternatives with low-MET, such as models characterized by R-parity violation, compressed spectra, and hidden valleys. In particular, the "stealth SUSY" model yields a low-MET signature while conserving R-parity by means of a new hidden sector in which SUSY is approximately conserved. I will present recent LHC searches for stealth SUSY, and discuss interesting areas for study at 13 TeV.
    When: Thu, March 5, 2015 - 1:00pm
    Where: PSC 3204
  • NO CNAM Cond. Matter Colloquium
    2015 APS MARCH MTG.
    When: Thu, March 5, 2015 - 2:00pm
  • Bianchi identities and (super)Lie algebra cohomology
    Speaker: Stephen Randall and William Linch
    Abstract: We'll discuss how (super)Lie algebra cohomology makes it possible to organize all the Bianchi identities for superforms, which previously didn't appear to follow any particular pattern. Reference: arXiv:1412.4686.
    When: Thu, March 5, 2015 - 3:30pm
    Where: PHY 1117
  • Particle Astrophysics Seminar
    Speaker Name: Dr. Rachel Carr

    Speaker Institution: Columbia University

    Title: Entering the Two-Detector Phase of the Double Chooz Experiment

    Abstract: In 2011, Double Chooz became the first reactor-based experiment to indicate a nonzero value of the neutrino mixing parameter theta_13. This observation was made with a single detector located approximately 1 km from the two cores of the Chooz Nuclear Power Plant in northeastern France. Since then, we have increased the precision of our single-detector theta_13 measurements through a variety of novel techniques. Now, as our near detector takes its first months of data, we can begin to suppress the reactor flux uncertainty which dominated previous analyses. I will report the most recent Double Chooz results, projected reach in theta_13, and prospects for additional physics measurements.

    When: Fri, March 6, 2015 - 3:00pm
    Where: PSC 3150
  • JQI Seminar
    Speaker Name: Birgitta Whaley

    Speaker Institution: UC Berkley

    Title: Novel collective states of molecules and macroscopic superpositions

    Abstract: While quantum correlations in dipole-coupled arrays of molecules can enhance light-matter interactions, resulting in superradiance, little is known about how their spectroscopic properties change when the dipole-coupling is strong enough to cause electronic polarization. In the first part of this talk I shall analyze a linear array of dipole-coupled molecules that shows a spectroscopic signature of a quantum phase transition between regimes of weak and strong coupling, corresponding to paraelectric and ferro/antiferroelectric polarized phases. The linear absorption is found to show increasing superradiant enhancement as the phase transition is approached and is singular at the transition, after which it displays a quadratic ‘hyperradiant’ size scaling of one-photon absorption and emission in the strong coupling regime. Possibilities for emulating this unusual strong coupling phase and its anomalous superradiance will be discussed. In the second part of the talk I shall summarize recent results systematizing the size of macroscopic superposition states that have led to generalization of the energy-time uncertainty relation to arbitrary quantum states, with implications for the minimal speed of quantum transformations.
    When: Mon, March 9, 2015 - 11:00am
    Where: CSS 2400
  • EPT Seminar
    Title: The Galactic Center GeV Gamma-ray Excess: Have We Started to See Dark Matter?

    Speaker: Sam McDermott, Stony Brook University

    Abstract: Recent claims of an excess of gamma rays from the Galactic center have grown in statistical significance over the last few years. In this talk, I’ll provide a (fairly optimistic) summary of the observational and phenomenological work relating to the Galactic center GeV excess. This will necessitate an up-to-date discussion of the claims in the literature, and will also include discussion of some particle physics models that can provide a basis for the signal. I’ll go on to discuss ideas for new techniques that might help push us toward a deeper understanding of the signal and its phenomenology.
    When: Mon, March 9, 2015 - 4:00pm
    Where: PSC 3150
  • Space and Cosmic Ray Physics Seminar
    Speaker Name: Peter Yoon

    Speaker Institution : IPST, University of Maryland

    Title : Plasma Emission by Nonlinear Electromagnetic Processes

    Abstract : The plasma emission is the radiation mechanism responsible for solar type II and type III radio bursts. These radio bursts are important in that they may be used in the space weather forecasting effort, which is a research topic of contemporary importance. The detection of radio bursts from the Sun in the meter wavelengths were first carried out in the 1940s. Identification and classification of different types of solar radio emissions into type I, II, and III, were subsequently done in the 1950s. Subsequently, further classification and identification of type IV and V radio bursts were added in the 1960s. The first theory of plasma emission, which was put forth to explain the type II and III radio bursts, came in 1958 by the Soviet scientist Vitaly Ginzburg, and further developed by others in the 1970s and 1980s, and well into the 1990s. As a result, the standard paradigm was established in which, the complicated radio emission process first involves energetic electrons produced at the solar active region during the flare. As the energetic electrons stream outward following open magnetic field lines, they interact with the dense background solar wind plasma. The beam-plasma interaction excites electrostatic Langmuir waves via the well-known bump-on-tail instability, followed by nonlinear processes of wave decay and scattering, eventually leading to the backward-propagating Langmuir waves as well as low-frequency ion-acoustic waves. The generation of EM radiation is a byproduct of the nonlinear processes. Partial conversion of electrostatic wave energy, primarily residing in the form of Langmuir turbulence, to transverse EM wave energy is called the plasma emission process, and the resultant radiation emission occurs at the plasma frequency and/or its harmonic(s). Such an elaborate process can, in principle, be demonstrated on the basis of EM weak turbulence theory, the fundamental equations thereof and their derivation can be found in the literature and in the
    papers by the present author. However, the complete numerical solution of the entire set of EM weak turbulence equations has not been done until quite recently, when the present author and his colleagues [Ziebell, Yoon, et al., 2014, 2015] numerically solved the complete equations for the first time. Until then, various approximations and simplifications have been made. This talk will overview the solar radio emission phenomenon and the recent theoretical development.

    When: Mon, March 9, 2015 - 4:30pm
    Where: CSS 2400
  • Informal Statistical Physics Seminar
    Speaker Name: Dr. Andre Cardoso Barato

    Speaker Institution : University of Stuttgart

    Title : Thermodynamic Uncertainty Relation for Biomolecular Processes

    Abstract : Biomolecular systems like molecular motors or pumps, transcription and translation machinery, and other enzymatic reactions can be described as Markov processes on a suitable network. We show quite generally that in a steady state the dispersion of observables like the number of consumed/produced molecules or the number of steps of a motor is constrained by the thermodynamic cost of generating it. An uncertainty ε requires at least a cost of 2kBT/ε2 independent of the time required to generate the output. We also obtain a lower bound on the Fano factor, which is an observable quantifying fluctuations that can be measured in single molecule experiments. This lower bound depends on the affinity driving the process out of equilibrium

    When: Tue, March 10, 2015 - 1:15pm
    Where: Room 1116, IPST Building, Bldg 85
  • CMTC Seminar
    Speaker: Vladimir Juricic (Utrecht University, The Netherlands)

    Title: Topological Crystalline Quantum Matter

    Abstract: Topological band insulators are bulk insulating states of matter, which in the presence of time-reversal symmetry feature metallic states at their edge or surface.
    This state of quantum matter has been experimentally realized in the HgTe/CdTe quantum wells and various (mostly) Bismuth-based compounds.

    I will first introduce the concept of topological band insulators and then discuss the role of crystal symmetries in the physics of these states of quantum matter. I will derive the classification of topological band-insulators protected not only by time-reversal, but also by space group symmetries [1]. As a result, there are three broad classes of topological states: (a) Gamma-states robust against general time-reversal invariant perturbations; (b) Translationally-active states protected from elastic scattering, but susceptible to topological crystalline disorder; (c) Valley (crystalline) topological insulators sensitive to both elastic and crystalline disorder. I will also discuss probing of the topological states in the bulk by magnetic pi-fluxes and lattice dislocations both in two [2] and three dimensions [3].
    Finally, some experimental implications of our classification scheme will be considered.

    [1] R.-J. Slager, A. Mesaros, V. Juricic, and J. Zaanen, Nature Physics 9, 98 (2013).
    [2] V. Juricic, A. Mesaros, R.-J. Slager, and J. Zaanen, Phys. Rev. Lett. 108, 106403 (2012).
    [3] R.-J. Slager, A. Mesaros, V. Juricic, and J. Zaanen, Phys. Rev. B 90, 241403(R) (2014).

    Host: Bitan Roy
    When: Tue, March 10, 2015 - 2:00pm
    Where: 2205 Toll Physics Bldg.
  • Physics Colloquium - Michael Brown
    Speaker Name: Michael Brown

    Speaker Institution: Swarthmore College

    Title: A career as a physicist at a liberal arts college: a 20 year retrospective

    Abstract: The goal of this talk is to give an overview of the benefits and demands of a career of a physicist at an undergraduate-only liberal arts college. The perspective will be from my 20 year career as a plasma physicist at Swarthmore College, while drawing on contacts and visits from many other liberal arts colleges around the country. A liberal arts college professor is both teacher and scientist, but always with an eye towards mentoring undergraduates. I'll draw on examples from my own research on plasma turbulence and reconnection on the SSX device, as well as 20 years of teaching at Swarthmore.

    hosted by Howard Milchberg
    When: Tue, March 10, 2015 - 4:00pm
    Where: PSC Lobby
  • CMTC Seminar
    Speaker: Raquel Queiroz (Max Planck Institute, Stuttgart)

    Title: Strongly disordered topological superconductors without inversion center

    Abstract: Noncentrosymmetric superconductors with strong spin-orbit coupling and the B phase of He-3 are possible realizations of topological superconductors with time-reversal symmetry. The nontrivial topology manifests itself at the material’s surface in terms of surface bound states, strongly dependent on the momentum dependence of the order parameter. We show that disorder can be a useful tool to experimentally identify and distinguish different types of surface states, and, using extensive numerical simulations, we investigate the stability and properties of such states under strong surface disorder, influencing both bulk and surface states.

    Of particular interest are the linearly dispersive helical Majorana modes of fully gapped superconductors, protected from disorder weaker than the superconducting gap. A critical crossover from weak to strong disorder is observed in both two and three dimensions, through which an extended state exactly at zero energy always persists. We contrast these results with the linear dispersive surface states of Z2 topological insulators.

    Host: Philip Brydon
    When: Wed, March 11, 2015 - 11:00am
    Where: 2205 Toll Physics Building
  • Refreshments for CNAM Colloquium

    When: Thu, March 12, 2015 - 1:30pm
    Where: The "new" Toll Room, Phys. Rm 1305F
  • CNAM Cond. Matter Colloquium
    Speaker Name: Prof. Jens Koch

    Speaker Institution: Northwestern

    When: Thu, March 12, 2015 - 2:00pm
    Where: Phys Rm 1201
  • Witten's paper on integration on supermanifolds, part 1
    Speaker: Matt Calkins
    Abstract: We will begin talking about E. Witten, "Notes On Supermanifolds and Integration", arxiv:1209.2199.
    When: Thu, March 12, 2015 - 3:30pm
    Where: PHY 1117
  • Materials Science and Engineering Seminar
    Speaker Name: Paula Mellado

    Speaker Institution: Adolfo Ibañez University, Santiago, Chile

    Title: Bio-inspired microuidics: The case of the velvet worm

    Abstract : The rapid squirt of a proteinaceous slime jet endows the ancient velvet worms (Onychophora) with a unique mechanism for defense from predators and for capturing prey by entangling them in a disordered web that immobilizes their target. However, to date neither qualitative nor quantitative descriptions have been provided for this unique adaptation. We have investigated the mechanism that allows velvet worms the fast oscillatory motion of their oral papillae and the exiting liquid jet that oscillates with frequencies ƒ ~ 30 – 60 Hz. Using anatomical images and high speed videography, we show that even without fast muscular action of the papilla, a strong contraction of the slime reservoir and the geometry of the reservoir-papilla system suffices to accelerate the slime to speeds up to ν ~ 5 m/s in about ∆t ~ 60 ms. A theoretical analysis and a physical simulacrum allow us to infer that this fast oscillatory motion is the result of an elastohydrodynamic instability driven by the interplay between the elasticity of oral papillae and the fast unsteady flow during squirting. Inspired by the physics of the velvet worm squirting system we propose several applications that can be implemented using this instability. Ranging from high-throughput droplet production, printing, micro-nanofiber production between others.
    When: Fri, March 13, 2015 - 1:00pm
    Where: Room 2110, Chemical and Nuclear Engineering Bldg.
  • JQI Special Seminar
    Speaker Name: Mark Fischer

    Speaker Institution: Weizmann Institute of Science

    Title: A macroscopic 'order parameter' for many-body localization

    Abstract: Recent theoretical progress in characterizing many-body localized systems has not been confronted so far with an experimental test. I will present a theoretical analysis of new experimental results showing many-body localization of interacting fermions in a quasi periodic optical lattice potential (arXiv:1501.05661). Specifically we considered the time evolution of a system prepared in a particular many-body initial state, a charge-density wave. Relaxation of the density-wave to a non-vanishing value at long times provides a direct demonstration of the breakdown of ergodicity in the many-body localized state and the saturation value can serve as an order parameter of this state. We found this stationary density wave order to show a distinctive dependence on the interaction strength, in agreement with experiment. Moreover, I will discuss how (temporal) fluctuations in this order parameter are connected to the entanglement-entropy growth, thus providing a distinguishing signature that could be observed in future experiments.
    When: Mon, March 16, 2015 - 2:00pm
    Where: PSC 2136
  • CMTC Seminar
    Speaker: David Abergel (Nordita)

    Title: Tunneling conductance in strongly correlated materials.

    Abstract: Tunneling conductance measurements such as two-terminal transport and scanning tunneling microscopy are important tools for the characterization of condensed matter systems. However, for strongly correlated materials, the tunneling mechanism has not yet been theoretically reproduced or adequately explained. This is because the combination of strong electron-electron interactions and the non-equilibrium nature of the problem is poorly understood. In this talk, we show that a new theory for the tunneling conductance for strongly correlated systems can reproduce all the features of experimental data for many different materials, and show explicit comparisons for a wide variety of materials. In particular, our theory gives a quantitative fit and a qualitative explanation for the side peaks which are present in many different experimental data, but which are not explained by any prior theory.

    Host: Jay Sau
    When: Tue, March 17, 2015 - 11:00am
    Where: 2205 Toll Physics Building
  • Spring Break- No Physics Colloquium

    When: Tue, March 17, 2015 - 4:00pm
    Where: PSC Lobby

Department of Physics

University of Maryland
College Park, MD 20742-4111
Phone: 301.405.3401
Fax: 301.314.9525