Fall 2016: Colloquium Series

Talks are usually scheduled on Thursdays during common hour (12:50 – 1:50 PM) in Room N304 of the Science and Engineering Building, unless otherwise indicated. Lunch is served starting at 12:20PM. All are welcome!

Thursday September 08, 2016
1st week of classes : No talk scheduled

Thursday September 15, 2016

Summer Student Poster Day

The department hallways will be decorated by posters by Union College physics majors who participated in summer research this year. The authors will stand by their posters to discuss their work and answer our questions while we all enjoy lunch during our first official colloquium of the new academic year.

Thursday September 22, 2016

Few-Layer Black Phosphorus: a Material with tunable properties

Vincent Meunier
Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute

Black phosphorus (or “phosphorene” at the monolayer limit) has attracted significant attention as an emerging 2D material due to its unique properties compared with well-studied graphene and transition metal dichalcogenides such as MoS2 and WSe2. In bulk form, this monoelemental layered structure is a highly anisotropic semiconductor with a bandgap of 0.3 eV which presents marked differences in optical and electronic properties depending on crystalline directions. In addition, black phosphorus possesses high carrier mobility, making it promising for applications in high frequency electronics. A large number of characterization studies have been performed to understand the intrinsic properties of BP. Here I will present a number of investigations where first-principles modeling was combined with scanning tunneling microscopy (STM), Raman spectroscopy, and transmission electron microscopy (TEM) to assist in the design of phosphorene-based devices.

Thursday September 29, 2016

Dark matter: All your questions answered…with more questions!

Matthew Bellis
Department of Physics and Astronomy, Siena College

Over the last 50+ years, we have definitively learned that the motions of galaxies and clusters and the curvature of light on cosmological scales cannot be explained solely by the gravitational attraction of the baryonic matter in the universe. The leading theory to explain this discrepancy proposes a particle that does not interact through the strong or electromagnetic interaction: dark matter. However, no definitive experimental evidence for this particle has been found. This talk will give an introductory overview of the experimental searches for dark matter with an emphasis on WIMP (Weakly Interacting Massive Particle) models.

Wednesday October 05, 2016

Amorphous Materials:  From Two-Dimensional Glass to Bubble Rafts

Kristen M. Burson
Physics Department, Hamilton College

Glass is a pervasive material in daily life, from windows, to fiber optics, to kitchen ware.   Due to the abundant utility of glass there is much interest in answering the question: “What is the atomic structure of glass?” For crystalline materials, diffraction techniques can be used to determine the atomic configuration. But glass evades definitive atomic structure determination with the same techniques because it is complex and amorphous. SiO2 in its amorphous form is commonly known as glass for every-day uses. In this talk I’ll discuss recent work to determine the atomic structure of glass using scanning probe microscopy. I’ll show atomic resolution images of bilayer silica (SiO2), a model for glass, and present an assessment of the structure of model glass under application relevant conditions. Finally, this talk will explore the similarities between glass and other amorphous networks with special emphasis on a comparison between millimeter-scale bubble raft network structures and the atomic-scale silica network structure.

Thursday October 13, 2016

Mechanics of Fibrous Materials

Catalin R. Picu
Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute

Many biological and man-made materials have a fiber network as their structural component. Examples from the living world include the cellular cytoskeleton and various types of connective tissue. Examples from the non-living world include paper, rubber, insulation and consumer products, such as baby diapers. In this presentation I will review the mechanical behavior of various materials of this type. Further, the relationship between the microstructure and the mechanical properties of the network will be outlined, with emphasis on identifying regimes in which large changes of the system scale behavior are triggered by small changes of the system parameters. The discussion will underline differences between the behavior of fibrous materials and that of continuum bodies.

Thursday October 20, 2016

Phyllosilicate Emission from Protoplanetary Disks – The Indirect Detection of Extrasolar Water

Melissa Morris
Physics Department, SUNY Cortland

morrisabstract_phyllosilicatesPhyllosilicates are hydrous minerals formed by the interaction between rock and liquid water and are commonly found in meteorites originating in the asteroid belt. These products of aqueous alteration of primitive planetesimals are believed to be the source of the majority of Earth’s water. The spectrum of the zodiacal dust in our Solar System (thought to result from collisions of planetesimals and sublimation of comets) has been modeled with the inclusion of phyllosilicates. Collisions between planetesimals in extrasolar protoplanetary disks may also produce dust containing phyllosilicates, indicating the presence of liquid water. It has been demonstrated that the characteristic emission features of these hydrous minerals are detectable in the infrared using instruments on board the Spitzer Space Telescope. In this talk, I discuss the phyllosilicates commonly found in meteorites, and describe our simple 2-layer radiative transfer disk code used to produce model spectral energy distributions (SEDs) of disks. I discuss how archived data from the Spitzer Space Telescope can be used to compare model SEDs of protoplanetary disks to observations. In this manner, we can determine whether liquid water is indicated in these extrasolar systems, and therefore, the possibility for life.

Thursday October 27, 2016

Explorations in the Geometry of Thinking

Kurt Przybilla
The Molecularium Project, Rensselaer Polytechnic Institute

Model building inspired by the works of  Buckmister Fuller, the visionary inventor of geodesic domes and namesake of “Bucky Balls”,  led to the accidental discovery and patenting of the world’s first spinning tops with more than one axis of spin.  Co-creator, writer and producer of the Molecularium Project at RPI, Kurt Przybilla, shares a fast-paced, fun story of tetrahedrons, toys and the primary structural systems of the Universe.

Thursday November 03, 2016

String Theory in the Age of Duality

Cindy Keeler
Neils Bohr Institute

After a brief review of string theory and its genesis as a “Theory of Everything”, we will discuss the nature and use of dualities in modern string theory and quantum gravity. Dualities provide two (often very different!) descriptions of the same physical system.  We will study an example of duality in Maxwell’s equations, and then explore how these dualities have led to broad applications of string-inspired physics, far beyond its initial high energy physics beginnings.

Thursday November 10, 2016

From Ultracold Plasmas to White Dwarf Stars

Thomas C. Killian
Department of Physics & Astronomy, Rice University, Houston, TX 77005

Some of the most extreme environments in the universe can be described as strongly coupled plasmas, which are characterized by an average Coulomb interaction energy between neighboring particles that exceeds the thermal kinetic energy. This is the case in dense laboratory and astrophysical plasmas, such as in inertial-confinement-fusion experiments, white dwarf stars, and gas-giant-planet interiors. Strong interactions limit our ability to model and understand these systems because they violate fundamental assumptions underlying the standard theoretical description of collision rates and transport coefficients. They also lead to spatial correlations and surprising equilibration dynamics. I will describe how we can study the physics of strongly coupled plasmas in a system created by photoionizing laser-cooled atoms [1]. This creates the coldest neutral plasmas in existence, with temperatures barely one degree above absolute zero. Strong coupling is obtained at relatively low density, which slows the dynamics and makes short-timescale processes (compared to the inverse collision rate) experimentally accessible. This combination of atomic and plasma physics opens a new direction in the study of “dense” plasmas, which has traditionally been the playground of astrophysics and large national facilities. In particular, I will describe recent experiments studying the breakdown of standard kinetic theory and the measurement of self-diffusion [2,3].

This work is supported by the National Science Foundation, Department of Energy, and the Air Force Office of Scientific Research.

[1] “Ultracold Neutral Plasmas,” T. C. Killian and S. L Rolston, Phys. Today 63, 46 (2010).
[2] “Velocity relaxation in a strongly coupled plasma,” G. Bannasch, J. Castro, P. McQuillen, T. Pohl and T. C. Killian, Phys. Rev. Lett. 109, 185008 (2012).
[3] “Experimental measurement of non-Markovian dynamics and self-diffusion in a strongly coupled plasma,” T. S. Strickler, T. K. Langin, P. McQuillen, J. Daligault, and T. C. Killian, arXiv.org/1512.02288 (2015).

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