Spring 2013 Seminars
All Physics Seminars are held in S-3-126 at 2:00pm unless otherwise noted
Wednesday, January 30
Stochastic inference of regulatory networks inside living cells
In the noisy cellular environment many mRNA and protein species occur at low integer molecular counts, and hence are subject to large stochastic fluctuations in copy numbers over time. Far from being a hindrance, signatures of protein/mRNA noise levels can be informative about the underlying gene network topology. In this talk, I will present recently developed mathematical techniques that harness fluctuations in the levels of biochemical species for systems identification of gene regulatory networks. Finally, I describe our current efforts is using these techniques for reverse engineering the genetic circuitry of the Human immunodeficiency virus (HIV).
Wednesday, February 6
Northeastern University Boston
Directed Assembly Methods for Manufacturing Nano Enabled Devices
Directed assembly of nanoparticles has been shown to be a promising approach for building functional nanomaterials and nanostructures towards potential applications in areas such as optics, electronics, and sensors. At the NSF Center for High-rate Nanomaufacturing, we have developed a suite of room temperature and pressure processes for assembling various nanoelements such as nanotubes, nanoparticles and nanosheets at desired location on a variety of substrates with a desired orientation and density. In this presentation, I will focus on electric field assisted directed assembly methods for fabricating both 2D and 3D architectures made of carbon nanotubes (CNTs) and nanoparticles. Parameters that primarily influence the assembly results for various architectures and substrates will also be discussed. Incorporation of these assembled architectures into devices such as chemical sensors, biosensors, electronic devices, interconnects, energy harvesters and NEMs, devices etc. and the resulting device performance will be compared to their commercial counterparts. These developed directed assembly processes are expected to lower current manufacturing cost of these devices of by two orders of magnitude.
Sivasubramanian Somu Ph.D. is a Research Scientist in the NSF NSEC Center for High-Rate Nanomanufacturing at Northeastern University in Boston, Massachusetts, USA. He has authored more than 50 papers in journals and conference proceedings and serves as a referee for various science and engineering journals. He has more than ten years of experience in standard CMOS fabrication and characterization methods for solid-state devices, nano-electro mechanical systems and various magnetic devices. His current projects include Bi-stable Nanoswitch, single-walled carbon nanotube-based multifunctional chemical and biosensors, high power density energy storage systems and electronic transport studies in SWNTs. He received his PhD degree in physics from Northeastern University.
Wednesday, February 13
Washington State University
Quasi-One-Dimensional Quantum Gases: Effective Interactions, Energetics and Correlations
Since the first experimental realization of gaseous atomic Bose-Einstein condensates in 1995, the field of cold atom physics has progressed and matured tremendously. Nowadays, the interaction strength of cold atom systems can be tuned essentially at will and the confinement geometry can be adjusted. This talk will summarize theoretical studies of quasi one-dimensional harmonically trapped atomic gases. A model Hamiltonian with effective one-dimensional atom-atom interactions will be introduced and its validity will be benchmarked. The excitation spectrum and two-body correlations of small two-component Fermi gases will be analyzed as a function of the interspecies interaction strength. The changes of the structural expectation values reveal an intriguing interplay between the interspecies interactions and the Pauli exclusion principle, which can be thought of as corresponding to an effective intraspecies repulsion. It is suggested that the observed structural changes may be interpreted as a smooth few-body analog of the transition from a non-magnetic to a magnetic phase. Implications of our theoretical studies for ongoing cold atom experiments will be discussed.
Friday, February 22
Cascading failures of interdependent networks
Complex networks appear in almost every aspect of science and technology. So far the network theory has focused mainly on isolated networks, but many real-world networks do in fact interact with and depend on other networks. Very recently an analytical framework for studying the percolation properties of interacting networks has been developed. Here we review the analytical framework and the results for percolation laws for a network of networks (NON) formed by n interdependent random networks. The percolation properties of a network of networks differ greatly from those of single isolated networks. In particular, networks with broad degree distributions, such as scale free networks, that are robust when analyzed as single networks become vulnerable in a NON. Moreover, in a NON, cascading failures appear due to dependency of nodes in different networks on one another. When there is strong interdependent coupling between the networks, the percolation transition is discontinuous (is a first-order transition), unlike the well-known continuous second-order transition in single isolated networks. These results should prove relevant to a wide range of disciplines in which percolation and network theory are factors.
Wednesday, February 27
In this presentation, I will give an overview of the history of the ideas related to solitons, from John Scott Russell's serendipitous empirical discovery in 1834, through Zabusky and Kruskal's numerical re-discovery in 1965 and Lax's insight of 1968 towards the all-enveloping ideas of Zakharov-Shabat and Ablowitz-Kaup-Newell-Segur emerged in 1972-73. Whenever possible, I will try to establish links between the formal theory of integrable partial differential equations and familiar objects of Quantum Mechanics and Laser Physics. In this spirit, I'll first review a relatively well-known connection between the Korteweg-de Vries solitons and the Poeschl-Teller potential (sech^2(x) well). I'll further proceed to introduce an entirely unrecognized bridge between the sine-Gordon and Nonlinear Schroedinger solitons and two-level atom under under a sech(t) laser pulse. Both examples can be used to visualize the defining property of the solitons, their mutual transparency. If time permits, I'll briefly review our recent results on two completely mutually unrelated connections between the solitons and the supersymmetic quantum mechanics (SUSY-QM).
Wednesday, March 6
Lighting up the Way of Energy Sustainability
Energy sustainability has become a critical challenge for the modern society. Energy efficiency and renewable energy are the “twin pillars” of sustainability. In this talk we present applications of nanophotonics in both aspects: (1) Electronic-photonic synergy for Green Information Technology, in which the advantages of photons in energy-efficient, high bandwidth data transmission is combined with those of electrons in high capacity data processing on a single microchip; (2) Self-assembled nanophotonic structures for efficiency enhancement in thin-film solar cells and concentrated solar power (CSP) systems. Efficiently manipulating radiated electromagnetic energy, nanophotonics will “light up” the future of energy sustainability.
Wednesday, March 13
University of Massachusetts, Boston
The energy cost of measurement is the work value of the acquired information
The energy cost of measurement is an important fundamental question, and may have profound implications for quantum technologies. In the context of Maxwell’s demon, it is often stated that measurement has no minimum energy cost, while information has a work value. However, as we elucidate, the first of these statements does not refer to the cost paid by the measuring device. Here we show that it is only when a measuring device has access to a zero temperature reservoir — that is, never — that measurement requires no energy. To obtain a given amount of information, all measuring devices must pay a cost equal to that which a heat engine would pay to obtain the equivalent work value of that information.
Wednesday, March 20
Wednesday, March 27
Consejo Superior de Investigaciones Científicas, Spain
Controlling quantum systems in circuit QED designs
The field of circuit QED is widely considered the on-chip realization of cavity QED, where superconducting artificial atoms and microwave photons interact at the quantum level. The large tunability attainable in these solid-state devices, has made possible the achievement of the the so-called strong and ultrastrong coupling between light and matter. In this talk, I will show how we can take advantage of this large degree of control in circuit QED to manipulate the light-matter interaction, and ultimately the microwave photons in a resonator or propagating in an open transmission line. This offers a wide range of applications, ranging from quantum communications, condensed matter physics, to simulations in Quantum Field Theory.
Friday, March 29
Breaking an electron: Spin incoherent behavior in strongly correlated low dimensional systems
Electrons are fundamental building blocks of nature and are indivisible in isolation. However, when electrons (or other quantum particles with an internal "spin" degree of freedom) are confined in one spatial dimension, they may lose their identity as individual particles, and "break'' into separate excitations carrying spin, and charge, with each degree of freedom being characterized by a different energy scale. While the basic theoretical understanding of spin-charge separation in one-dimension, known as "Luttinger liquid theory'', has existed for some time, recently a previously unidentified regime of strongly interacting one-dimensional systems at finite temperature came to light: The "spin-incoherent Luttinger liquid". This occurs when the temperature is larger than the characteristic spin energy scale. The key to establishing both Luttinger liquid behavior and spin-incoherent Luttinger liquid behavior in experiment is detailed knowledge of the spectral properties.
Friday, April 5
From Scale Invariant Theories to Quantum Gravity in Curved Space
Theories which exhibit exact scale invariance have played a crucial role in our understanding of nature. Indeed, they describe systems near a second order phase transition or near a quantum critical point. In some cases, such systems enjoy a larger symmetry, called conformal symmetry. After reviewing some aspects of conformal symmetry, I will describe an exciting connection, which over the last decade has become an active area of research. Namely, the description of conformal invariant theories in terms of quantum gravity in curved space.
Wednesday, April 10
University of Central Florida
Physics and chemistry of graphene: controlling experiments down to atomic scale
Nanoscale materials are sensitively influenced by atomic scale defects and adsorbates. Such sensitivities can be used to impart various functionalities to develop new device technologies, but they can also introduce a large uncontrollable variability to measurements masking the intrinsic properties. As such, my laboratory uses a unique approach to control experiments down to atomic scale. I will discuss our results on the native carrier scatterers in graphene on SiO2, the relationship between friction and surface diffusion on graphene, and the structure of a peptide on graphene surface.
Wednesday, April 17
Institute for Theoretical Atomic, Molecular, and Optical Physics
Harvard-Smithsonian Center for Astrophysics
Manipulating quantum states in ultracold gases using conservative and nonconservative forces
Friday, April 19
postponed to May 3
Fate of the Kinetic Ising Model
Wednesday, April 24
Efficient numerical methods for high-frequency eigenmodes and diffraction problems
In the first part, we overview recent work on numerical computation of high-frequency modes (eigenstates) of cavities, based upon the so-called Dirichlet-to-Neumann map and integral operators on the boundary. This is an improved variant of the "scaling method", one which also allows rigorous error analysis. As an application we show recent work studying chaotic nodal domain statistics. In the second part we overview the use of integral equations (sometimes known as boundary element methods) for time-harmonic wave scattering from piecewise-homogeneous materials, in 2D and 3D. We focus on periodic structures such as arrays and gratings. Applications include nano-scale optical devices and solar cells. Conventional periodic integral equation solvers break down at so-called Wood's anomalies; we present new formulations that are robust, and which exploit the fast multipole method and iteration to solve problems with O(N) effort, where N is the number of unknowns.
Friday, April 26
Kamal Alavi, PhD
Senior Engineering Fellow, Raytheon Company
Evolution of RF Power Transistors: From Si BJT to GaN HEMT
RF power is used in communication, radars, and heating. In this talk, the basic and fundamental device and material aspects of transistors for RF power generation will be reviewed in a rigorous and yet easy to understand way. Similarity and differences between requirements for RF power, VLSI, and power switching will be discussed. Technological trends and presently known ultimate performance limitations of each device technology will be shown. Numerous examples form published data and vendor’s web site of commercially available RF transistors will be given to bench mark the present status of the industry. The newly arrived and disruptive gallium nitride HEMT technology fundamentals, that are different from all previous RF power transistor technologies, will be detailed using a vast body of published literature covering S to W band.
Kamal Tabatabaie-Alavi received the B.S. degree in electrical engineering from Sharif’s University of Technology, Tehran, Iran, in 1977 with emphasis on microwaves. He received M.S. and Ph.D. degrees in 1980 and 1984, respectively, from Massachusetts Institute of Technology, Cambridge, MA. His graduate work was on InGaAsP/InP based HBTs. He demonstrated the first InGaAsP hetero-junction photo transistor in 1979 and was winner of the IEDM best student paper award in 1982. In May 1984, he joined Raytheon Research Division, Lexington, MA. At Raytheon, he has been directly involved with process integration as well as device and process development of several generations of GaAs based technologies, including MESFETs, pHEMTs, and HBTs. He was the recipient of Raytheon Company 1996 Excellence in Technology award. He has served as chairman of Boston chapter of IEEE MTT society and session chair as well as panel chair for CSMANTECH conferences. He is an active member of technical program committee of CSMANTECH. He has authored and co-authored 23 technical papers and holds 12 US patents. His current interests are in GaN based FETs as well as co-integration of III-V compounds with Si. Dr. Tabatabaie-Alavi is a senior member of IEEE and a senior engineering fellow of Raytheon Company.
Wednesday, May 1
Jordan M. Horowitz
Thermodynamics with feedback: Extracting work from information
The laws of thermodynamics restrict the maximum efficiency with which a thermodynamic engine can convert heat into useful work. This limit, however, can be exceeded with the use of feedback, by altering the operational protocol of the engine in response to information about its microscopic state. In other words, information is a valuable resource for work extraction, much like free energy. In this talk, I will discuss recent results detailing how information enters into the thermodynamics of a system driven away from equilibrium by feedback, such as a thermodynamic engine. In particular, I will introduce and analyze a refinement of the second law of thermodynamics for discrete feedback, which connects information to heat, work, and irreversibility. We will see that optimal feedback processes that convert all the information into work are feedback reversible: they are indistinguishable from their time reverse. Finally, building on the intuition gained from examining the second law with feedback, I will introduce a prescription for designing optimal thermodynamic engines with feedback, which I will illustrate with an N-particle Szilard engine.
Friday, May 3
Fate of the Kinetic Ising Model
What could possibly be new in the Ising model, arguably the most-studied model of statistical physics? Plenty! Consider the Ising model initially at infinite temperature that is suddenly cooled to zero temperature and evolves by single spin-flip dynamics. What happens? In one dimension, the ground state is always reached and the evolution can be solved exactly. In two dimensions, the ground state is reached only about 2/3 of the time, and the long-time evolution is characterized by two distinct time scales, the longer of which arises from topological defects. In three dimensions, the ground state is never reached and the evolution is quite rich: (i) domains are topologically complex, with average genus growing algebraically with system size; (ii) the long-time state always contains "blinker" spins that can flip ad infinitum with no energy cost; (iii) the relaxation time grows exponentially with system size.
Wednesday, May 8
Venugopal Rao Soma
Advanced Centre of Research in High Energy Materials (ACRHEM)
University of Hyderabad
Laser-matter interaction: Laser Direct Writing and Laser Induced Breakdown Spectroscopic studies
The interaction of ultrashort (nanosecond/picosecond/femtosecond) pulses with materials is an extensive area of research with underlying, and often extremely rich, physics along with a variety of applications evolving from it. In this presentation we describe the interaction of laser pulses with materials and its implications in two parts (a) interaction of laser pulses with the bulk and surface of glasses and polymers producing micro- and nano-structures for microfluidic/lab-on-a-chip applications (b) ns and fs laser induced breakdown spectroscopic (LIBS) studies of HEMs towards understanding of molecular dynamics. Several useful applications resulting from these interactions will be discussed in detail.