Spring 2012 Colloquia
(Archive)
Our department colloquium is a forum for invited scientists to present modern research in a fashion accessible to those with a background in physics, but who are not experts in the field. Talks are aimed at the graduate level.
If you have questions about colloquium, please contact Dr. Anton Malko.
| Date | Speaker/Institution | Title/Abstract |
| Jan 18 Host: Bob Glosser |
Dr. Fred Tibbals, UTA/UTSW |
Wireless MEMS Sensing for Biomedical Physiology In this presentation we will review recent progress at UTSW and UTA in the development of MEMS based pressure sensors implanted in animal and human organ systems for monitoring physiological data relevant in clinical diagnosis, disease management, and medical research. For minimally invasive use of such systems in continual long-term medical monitoring the sensor should be implantable or insertable without requiring wires for communication or power outside the body. Design of MEMS and NEMS enables the fabrication of self-contained passive, batteryless, sensors which can be powered and interrogated by radiofrequency and/or optical electromagnetic radiation. A variety of sensors can be designed that couple force transduction modes with electromagnetic resonance characteristics varying as a function of applied pressure or tension, including piezoelectric, capacitive, electro-optical, inductive (resistance-inductance coupled) and others. We show how the biomedical requirements drive the design choices to match the technical characteristics of a sensor to a given monitoring application. We review the design considerations for pressure sensors in different types of biomedical applications, including monitoring for orthopedic fixation, wound healing, pressure sore prevention, uterine contractions, gastric, urological, ocular, intracranial/intraspinal, and vascular pressures, along with an overview of how nanoscale technologies have been applied to these areas as reported in the literature [1]. We present performance results obtained with some novel sensor designs and applications we developed in cooperative research at our medical and engineering institutions, for biomedical and pre-clinical research. References: [1] "Medical Nanotechnology and Nanomedicine", H. F. Tibbals, CRC Press, (2010). |
Jan 25 SLC 1.102 3:45 pm |
Dr. Han Htoon, LANL |
Single Nanocrystal Spectroelectrochemistry: A Probe for the Photo-Physics of Charged Nanomaterials. Presence of excess charges in quantum confined nanomaterials (NMs), such as semiconductor nanocrystals (NCs), nanowires (NWs), and single wall carbon nanotubes (SWCNTs) induces dramatic changes in their electronic structure and radiative/nonradiative recombination of carriers (electrons and holes). As a result, the key optical properties of NMs, such as photoluminescence spectrum and quantum yield are significantly altered. These effects of charging have been shown to be universal in previously studied NMs and are expected to affect in similar way in rapidly emerging, new NMs and complex nanostructures. In spite of importance and universality of charging effects, they are poorly understood at this moment. Here we demonstrate a novel approach capable of probing these effects directly. We have developed the single nanocrystal spectroelectrochemistry capability that allows monitoring the photoluminescence (PL) emission characteristics (i.e. PL intensity & lifetime) of a nanocrystal while it is charged and discharged reversibly by variation of electrochemical potential. This novel capability brings out the evidence that the well-known PL intermittency (blinking) behavior of NCs can arise via two distinct mechanisms. In the first case (type A), we identify that the blinking events can be closely correlated with rapid fluctuation in PL lifetimes. This type A blinking fall along the popular charging model of the blinking, which attribute the dark period of the NQD to the Auger quenching of charged exciton's PL emission. In the second case (type B), large changes in the PL intensity are found to be no longer accompanied by significant changes in PL dynamics. We proposed a new blinking mechanism that invokes interception of hot electrons by the surface states to explain this behavior. We further show that both blinking mechanisms can be controlled electrochemically and blinking can be completely suppressed under appropriate potential. These results illuminate the precise role of charging in blinking process. More importantly, this work also establishes the single NC spectroelectrochemistry as the effective tools for probing the photo-physics of charged nanostructures in general. |
Jan 30 TI Auditorium |
Dr. Stephen Powell, Joint Quantum Institute, University of Maryland Host: Dr. Myron Salamon |
Spin liquids and Higgs transitions in unconventional magnets Abstract: Conventional magnetic materials are disordered at high temperature and form ordered states when cooled. If such ordering is frustrated, an alternative "spin liquid" can appear at low temperatures. This phase displays a variety of surprising phenomena, which are described by a theory that parallels electromagnetism in the vacuum. A prominent example is the class of compounds known as "spin ice", where experiments confirm this description and also provide evidence of deconfined magnetic monopoles. Perturbations applied to such systems can relieve the frustration and cause ordering, and I will argue that the resulting transitions go beyond the standard Landau paradigm. They can instead be understood as Higgs transitions of an emergent gauge theory, which belong to a family of new universality classes. I will present theoretical predictions of such unconventional transitions in the spin ice materials, and supporting evidence from numerical simulations. |
Feb. 1 Host: Joe Izen++ SLC 1.102 3:45 pm |
Dr. Tapas Sarangi, U. of Wisconsin |
The Large Hadron Collider (LHC) has successfully delivered a large amount of data in the year 2011. ATLAS is one of the four major experiments designed to use these data to search for new physics phenomena like the Higgs Boson, Supersymmetry and microscopic Black Holes. In my talk the recent findings of the ATLAS experiment on the new physics searches will be discussed. While the world is excited by the tantalizing hints of the Higgs boson at the LHC, searches for evidence of physics beyond the Standard Model continue. One such search and one of the primary physics goals of the LHC is the search for Supersymmetry, a theory that predicts symmetry between matter and forces. It predicts a promising dark matter candidate, joining the physics of the very big to that of the very small. It provides a framework that unifies the fundamental forces. We will discuss the recent results of Supersymmetry searches at the LHC, its implications and its future prospects. |
Feb 8
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Prof. Chuanwei Zhang, Department of Physics and Astronomy, Washington State University, Pullman, WA | Title: Topological Quantum Materials at Nanoscale: a Roadmap to Majorana Fermions Prof. Chuanwei Zhang Department of Physics and Astronomy, Washington State University, Pullman, WA 99164 Abstract: Topological quantum matter has been an active research field in physics in the past three decades with numerous celebrated examples, including quantum Hall effect, chiral superconductor, topological insulator, etc. In topological materials, Majorana fermions, first envisioned by E. Majorana in 1935 to describe neutrinos, often emerge as topological quasiparticle excitations of the systems. Majorana fermions are intriguing because they can be construed as their own anti-particles and follow non-Abelian anyonic statistics under a pair-wise exchange of the many-particle wave function, unlike Dirac fermions where electrons and positrons (holes) are distinct. Although the emergence of Majorana fermions in solid state systems is by itself an extraordinary phenomenon, they have also come under a great deal of recent attention due to their potential use in fault tolerant quantum computation. So far most candidate systems for Majorana fermions suffer from one important problem: the required experimental parameters are beyond the capacity of current experiments. In this talk, I will show that nanoscale materials, such as hole-doped semiconductor nanowires or thin films, under certain external conditions, can support Majorana fermions in a regime of parameters already within experimental reach in routine experiments. A hole-doped nanowire or thin film, with its fundamentally different underlying physics from its electron-doped counterpart, also leads to many other topical advantages for realizing a topologically non-trivial state. Thus, these two systems are uniquely suited among all solid state systems for realizing and manipulating Majorana fermions in controllable experiments. |
Feb 15 3:45 pm SLC 1.102 |
Feb 15. Dr. Kerstin Hoepfner, RWTH Aachen University Host: Dr. Joe Izen |
Into Uncharted Territory-- New Physics at the LHC? The Large Hadron Collider (LHC) and its detectors have been designed to gain deeper insights into the structure of matter by colliding protons at the unprecentended energy of 7 TeV, about 3.5 times higher than what has previously been achieved. In these highly energetic collision, new particles and phenomena are predicted by a variety of theories and are actively being searched for with two multipurpose detectors - ATLAS and CMS. After 20 years of construction, the largest experimental endeavor humanity has ever undertaken started operating in 2010. Where are we after two years of data taking? Do we see signatures of new particles, like the long awaited Higgs? Is there evidence that elementary particles have a substructure and actually are not elementary? Do we observe black holes or other signs of extra dimensions? Many experimental searches have been performed allowing the LHC experiments to test and constrain theoretical models. A selection of these will be presented. |
Feb 22 3:45pm SLC 1.102 |
Dr. Jahred Adelman, Yale University |
An Excess of Needles in the Haystack? The Hunt for New Physics at ATLAS After the end of the LHC's 2011 proton-proton run, ATLAS is performing a wide range of exciting searches for new physics. I'll begin with a brief overview of the current state of the Standard Model, including some discussion of the many pieces of the theory that are incomplete or unsatisfactory. Next I will follow with some history of the techniques used for previous discoveries in particle physics, and will compare those analyses with the latest ATLAS searches; many, if not all, of the techniques are fundamentally the same. After discussing some more sophisticated searches for new physics, I will conclude with prospects for finding new physics during the 2012 LHC run. |
Feb 27 ECSS 2.102 |
Dr. Zhenyu Ye Host: Joe Izen |
Top-Quark Mass Measurements at DØ The top quark is the heaviest fundamental particle discovered so far. The large mass of the top quark, corresponding to a Yukawa coupling to the Higgs boson equal to unity within the uncertainty, suggests a special role for the top quark in the breaking of electroweak symmetry. The interest in the top-quark mass also arises from the constraint imposed on the mass of the Higgs boson from the relationship among the values of the top-quark mass, Higgs-boson mass and the radiative corrections to the W-boson mass. I will present the latest top-quark mass measurements by the DØ experiment at the Fermilab Tevatron proton- antiproton collider. |
| Feb 29 |
Dr. Ying Liu Space Science Lab. UC Berkley Host: Dr. Rod Heelis |
Evolution of CMEs from the Sun to interplanetary space: Building strategies for space weather forecasting Coronal mass ejections (CMEs) are the most spectacular eruptions in the solar corona and have been recognized as drivers of major space weather effects. They drive space weather typically in two ways. First, CMEs are often associated with a sustained southward magnetic field, which allows a strong coupling between the solar wind and the magnetosphere. Second, CMEs can generate interplanetary shocks, a key source of energetic particles and radio bursts. This talk will focus on some recent progresses in developing strategies to predict those effects, specifically: (1) Faraday rotation observations to determine the magnetic field orientation of CMEs; (2) combining MHD propagation of the solar wind with type II frequency drift to predict the arrival time of CME-driven shocks at the Earth; and (3) tracking and reconstruction of CMEs using coordinated in situ measurements and white-light observations from STEREO that can image CMEs continuously out to 1 AU. Event studies together with implications for instrumentation will be presented to demonstrate the capabilities with which the impact of a solar storm on the Earth can be predicted with small ambiguities. |
| Mar 7 | Dr. Mario Borunda, Harvard. Host: Myron Salamon |
"Imaging at the Nanoscale: exploring the quantum behavior of electrons inside nanostructures." I will present joint theoretical and experimental efforts aimed at understanding quantum coherent transport in graphene using scanning probe microscopy (SPM). The electronic properties of graphene are still under intense debate and the focus of many research efforts. In the first part of the talk, I will present our work on imaging coherent transport on graphene. Using SPM, our team was the first to image universal conductance fluctuations (UCF). For mesoscopic systems, the conductance fluctuates as a function of the chemical potential and the position of impurities. Our numerical simulations are in excellent agreement with the experiment and explain the features seen in graphene devices. In the second part of the talk, I will discuss our theoretical proposal towards achieving coherent control of interacting electrons in semiconductor quantum dots with the use of a SPM. The control of the charge states of electrons in quantum dots represent progress toward the manipulation of electrons for quantum information processing. These two systems provide a fascinating testbed for new physics and exciting opportunities for future applications based on quantum phenomena. |
| Mar 14 | ||
| Mar 21 | Dr. Fabiano Rodrigues Atmospheric and Space Technology Research Associates
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Remote sensing of the upper atmosphere/ionosphere using radars and GPS The variability of an important part of the upper atmosphere, the ionosphere, causes difficulties for various radio-based applications (e.g. over-the-horizon radars, synthetic aperture radars and GPS), but also provides unique opportunities for both fundamental and applied research of quiescent and turbulent plasmas. This presentation will give a brief overview of a few radio remote sensing techniques being used for studies of the ionospheric structure and variability including electron density irregularities. Focus will be given to techniques using different types of ground-based radars and techniques using observations made by ground-based and satellite-based GPS receivers. New and improved techniques for analyses of the observations will be described, followed by the presentation of new results. As we present these results, we will discuss their relevance for a better understanding of the upper atmosphere/ionosphere, and implications for a better specification of the so-called space weather. |
| Apr 18 | ||
| Apr 25 | ||
| May 2 | ||
| May 9 |
Archived Colloquia:
- Updated: July 18, 2012