University of Wyoming Physics & Astronomy Colloquium Series

Fridays -- 4:10 PM -- Prowse Room 234

Pre-Colloquium tea served at 3:45 in the southeast corner of the 2nd floor

Fall 2011 & Spring 2012 Schedule

Aug. 26 Ferromagnetic Nanoparticles
Professor J. Ping Liu (Department of Physics, University of Texas at Arlington)

Most ferromagnetic particles lose their hysteresis when their size is reduced to nanometer scale, except few hard magnetic materials like FePt and SmCo system compounds with extremely high magnetocrystalline anisotropy that can hold permanent magnetic moments at room temperature in small particles of several nanometers. By applying newly developed salt-matrix annealing and surfactant-assisted milling techniques, monodisperse ferromagnetic FePt, Sm-Co and Fe-Co nanoparticles have been successfully synthesized. These first-ever-available nanoparticles display various ferromagnetic properties at room temperature which are found to be strongly size dependent. The ferromagnetic nanoparticles are used as building blocks for advanced bulk and thin film magnets, and can be also applied in biomedical technologies. J. Ping Liu received his Ph. D degree in Applied Physics at the Van Der Waals Zeeman Institute, theUniversity of Amsterdam, the Netherlands in 1994. He is currently a Professorin the Department of Physics at the University of Texas at Arlington. His current work is focused on nanostrucutred bulk magnetic materials and magnetic nanoparticles. He has been the lead investigator of two joint research programs in nanocomposite magnets in the United States. He has authored or coauthored more than 170 peer-reviewed publications, including review articles, book chapters and a book. He has supervised more than twenty postdoctoral researchers and more than ten graduate students.

Sept. 23 Magnetic Nanoparticles For Applications of Nuclear Energy
You Qiang (Physics Department, University of Idaho, Moscow ID 83844, USA)

Future generation IV nuclear reactors in US and information storage medium in irradiation environment, and spent fuel recycling are expected to meet the standards of enhanced safety and economical compatibility. This talk is about our recent research contributes in part to meet this DOE mission: 1) Novel magnetic separation nanotechnology of ultrahigh selective conjugates of magnetic nanoparticle-chelator for spent nuclear fuel recycling. 2) Understanding of irradiation induced structural and magnetic property changes in magnetic nanoparticle films for recording medium in nuclear energy.

Sept. 28 Spin and charge dynamics in Heisenberg chains and the 1D Hubbard model
Fabian Heidrich-Meisner, LMU Munich, Germany

The spin-1/2 Heisenberg model is one of the prototypical models in the field of strongly correlated electron systems. Many of its properties, ranging from ground-state properties to thermodynamics, are very well understood since this model can be solved with the Bethe ansatz. The theory of its transport properties, however, is a resilient problem that has eluded a full solution for some decades already. For instance, there is no definite answer yet as to whether spin dynamics is diffusive or ballistic, as a function of temperature or interaction strength. In this talk, I will first give an overview of the current state-of-the-art in this field [1]. Second, I will describe our recent work on real-time spin and energy dynamics in this model [2,3]. Motivated by recent experiments we study the time-evolution of energy and spin density wave packets. This allows us to address the question of ballistic dynamics in the far-from-equilibrium regime. In a third part, I will turn to a related set-up, namely the sudden expansion of a two-component Fermi gas in an optical lattices [4], where similar physics emerges that can be studied in experiments with ultra-cold atomic gases.

[1] HM, Honecker, Brenig, Eur. Phys. J. Special Topics 151, 135 (2007)
[2] Langer, HM, Gemmer, McCulloch, Schollwoeck, Phys. Rev. B 79, 214409 (2009)
[3] Langer, Heyl, McCulloch, HM, arXiv:1107.4136
[4] Langer, Schuetz, McCulloch, Schollwock, HM, arXiv:1109.4364

Sept. 30 Atomistic simulation of charge transfer at photoexcited semiconductor surfaces
Dmitry Kilin (Department of Physics, North Dakota State)

Photo-excitations in functionalized semiconductor nano-structured surfaces lead to electron dynamics. These processes are modeled by the reduced density matrix method in the basis of Kohn-Sham orbital's. The energy of a photo-excitation is dissipating due to interactions with lattice vibrations, treated through the non-adiabatic coupling. [1,2] The electron/hole part of an excitation relaxes to the bottom of the conduction band /top of the valence band. The methodology is applied to surfaces of silicon and titanium dioxide, functionalized by minimalistic metal nano-clusters or by doping. Simulations of these models demonstrate the formation of charge transfer state. [2] These results are of the importance for an optimal design of nano-materials for photo-catalytic water splitting and solar energy harvesting.

Oct. 7 Ultrafast Electron Transfer from a Large Molecule to a Solid
Frank Willig - Fritz Haber Institut der Max Planck Gesellschaft Berlin, Germany

Light-induced electron transfer can be measured now with the time resolution of a few femtoseconds using commercially available instrumentation. Great flexibility has been achieved in preparing suitable systems since wet-chemistry preparation can be combined with preparations and measurements in ultra-high-vacuum. A large gap begins to narrow that separates ultrafast electron transfer of a small molecule on a metal surface from ultrafast electron transfer from a large molecule to a semiconductor surface. Investigations of the latter topic have long been performed applying traditional methods in photoelectrochemistry. Now, experimental techniques are available like femtosecond two-photon photoemission and femtosecond transient absorption. We report such data for perylene dyes on the surface of TiO2 and check on the compatibility of the time-resolved data with stationary optical spectra. The results highlight the ultrashort time scale and the dominant role of ultrafast non-adiabatic electron transfer. Model calculations have been performed by several groups applying different theoretical tools. Interesting new effects are predicted that have yet to be verified experimentally. Based on our experimental results we can make, however, a clear decision concerning the applicability of the different available theoretical model calculations to our specific experimental system. Experimental realizations of different ultrafast electron transfer dynamics appear feasible.

Oct. 14 Quantum dots: surface, ligands and photoinduced dynamics
Sergei Tretia (Los Alamos National Laboratory)

Over the years, electronic structure calculations, such as density functional theory (DFT), transformed theoretical chemistry and materials science by creating a new capacity to describe the electronic structure and complex dynamics in molecules with hundreds of atoms. This talk will overview our applications of modern quantum chemical methodologies to electronic structure of semiconductor nanocrystals. I will start with a brief introduction to DFT methodologies and their extensions to the xcited state calculations. Then I will analyze our benchmark of several computational methods versus high level ab initio techniques for the inimal CdSe clusters to assess an accuracy of different theories. Finally I will present our studies on the surface ligands effects on the QDs electronic structure, where we observe strong surface-ligand interactions leading to formation of hybridized states. This potentially opens new relaxation channels for high energy photoexcitations.

Oct. 21 Physics Based Growth of Nanorods
Hanchen Huang (Department of Mechanical Engineering, University of Connecticut)

Being key building blocks of various energy applications, nanorods are grown using physical vapor deposition. The growth process has become a common practice at research laboratories, but the physical principles have not been away from the focus of studies. In order to take the laboratory growth to engineering manufacturing, the growth process has to be controllable. The controllability will have to be enabled by the understanding of physical principles that govern the growth process. The understanding derives from a combination of density functional theory based ab initio calculations, classical molecular dynamics simulations, kinetic Monte Carlo simulations, and vapor deposition experiments. This seminar presents three recent advancements in understanding how nanorods grow at the atomic level. The first advancement pertains to a new surface diffusion mechanism; the second to a new mechanism of kinetic step bunching; and the third to a characteristic length scale of growing nanorods. The presentation will also include examples of impacts that the advancements have made or can make.

Oct. 28 Mapping the Universe with BigBOSS
David Schlegel (Lawrence Berkeley National Laboratory)

BigBOSS will produce the largest 3-D map of the Universe. Starting in 2017, BigBOSS will map 20 million galaxies and 4 million quasars at an average distance halfway across the visible Universe. From these maps, it will be possible to measure the expansion history and the effects of dark energy on that expansion to sub-percent precision. I will describe the current status of BOSS, a precursor project mapping 1.5 million galaxies using the Sloan 2.5-meter Telescope. BigBOSS increases this mapping capability with a 5000-fiber spectrograph on the 4-meter Mayall Telescope. I will describe the technical approach and challenges of this design.

Nov. 4 Exploring the Host Environments of Long-Duration Gamma-Ray Bursts
Emily Levesque (Einstein Postdoctoral Fellow, Department of Astrophysical and Planetary Sciences, University of Colorado at Boulder)

Long-duration gamma-ray bursts (LGRBs) are the signatures of extremely energetic phenomena occurring throughout our universe. These events have been proposed as possible tracers of star formation and metallicity evolution at high redshift; however, such an association is dependent on a thorough understanding of LGRB host environments and progenitors. In particular, the metallicity of LGRB host galaxies has become a matter of hot debate in recent years, with several studies suggesting that these events may be biased towards low-metallicity environments. We have conducted the first dedicated spectroscopic survey of LGRB host galaxies, determining a wide range of ISM properties for 17 z < 1 LGRB hosts and constructing the first mass-metallicity relation for LGRBs out to z ~ 1. We have also generated an extensive suite of new stellar population synthesis and photoionization models, tailored towards modeling the host environments of LGRBs. From this work, we conclude that LGRBs do exhibit a trend towards lower-metallicity host environments; however, we also detect several high-metallicity host environments and find no correlation between host metallicity and gamma-ray energy release in our sample. These results are at odds with previous theoretical and observational predictions. Additional studies of LGRB host galaxies, new generations of galaxy models, and an improved understanding of massive stellar evolution are all vital to understanding the progenitors and host environments that give rise to these enigmatic events.

Nov. 11 The First Direct Measure of BAL Quasar Orientations
Michael DiPompeo (Dept. of Physics and Astronomy, University of Wyoming)

Broad Absorption Line (BAL) quasars make up a significant fraction of the population of optically selected quasars, yet their nature is still debated. A common explanation for the presence of BALs in only a subset of all quasar spectra is orientation; it is often argued that these sources have high velocity outflows in an equatorial wind, and we only observe them when they are viewed more edge-on (farther from the accretion disk symmetry axis) than normal quasars. However, no direct measure of the orientation of these sources has been conducted, and several of their observational properties are difficult to explain with only geometrical arguments. This has led to a dichotomy in this area of study, where either BAL sources are seen from a particular viewing angle, or they are a particular evolutionary stage in the lifetime of all quasars. We have conducted a survey with the EVLA at two frequencies of BAL sources and a well-matched sample of unabsorbed quasars found in both SDSS and the FIRST survey. The goal was to measure the radio spectral index (α) of a large sample, as α is a statistical indicator of source orientation. We find that BAL quasars do show a significantly different spectral index distribution compared to normal quasars, though both have a large range, indicating that BAL sources cover a range of orientations but more often have higher viewing angles than non-BAL sources. We then performed Monte-Carlo simulations of these distributions to quantify the range of viewing angles to these objects. Finally, I will discuss the spectropolarimetric properties of BAL quasars and the relationship of these properties to the orientation of BAL quasars.

Nov. 18 Small Clusters of CdSe Nanocrystals: Intermittency, Interactions, and Insights.
Martin Gelfand (Dept. of Physics, Colorado State University, Ft. Collins)

The point of this talk is to describe what we have been able to learn from optical studies of small clusters of colloidal CdSe nanocrystals (NCs). The properties of individual NCs, in isolation, are mostly well-understood, while many potential applications are based on the behavior of large numbers of closely-packed NCs. By applying "single-molecule" spectroscopic methods to small clusters of NCs we have made progress in bridging the knowledge gap between one and many.

Jan. 20 Measuring Luminosity Dependent Quasar Clustering
Jessica Kirkpatrick (Astronomy Department, UC Berkeley)

Whether luminous quasars reside in dark matter halos of the same mass and accrete at different rates or live in haloes of different masses and accrete near the Eddington limit, is still an open question. I present measurements of the luminosity-dependence of quasar clustering, using data from the SDSS, 2SLAQ QSO and the new SDSS-III: BOSS Quasar surveys, allowing us to span ~4 magnitudes in luminosity, at a given redshift. Using a cross-correlation technique, we measure the clustering of ~3100 redshift 0.5 < z < 1.0 spectroscopic quasars with 6.0 million photometric galaxies, selected from the CFHT survey on Stripe-82 (CS82). We find a detection of luminosity dependent clustering in the cross-correlation and will discuss the amplitude of the clustering, as a function of redshift, luminosity, and black-hole mass of the quasar sample.

Feb. 10 How Quasars Work (and why you might care)
Gordon Richards (Department of Physics, Drexel University)

While it is now agreed that all massive galaxies harbor supermassive black holes, there is less agreement on how those black holes might influence the evolution of their host galaxies. Are the black holes passive members of the system or do they actively change the evolution of their host galaxies? I will discuss how the model of quasar physics has changed over the past decade, paying particular attention to the rise in popularity of accretion disk wind models. I'll argue that accretion disk winds play a much bigger role in quasar physics than is generally assumed and that understanding the variety of observed quasar properties is important not only for our understanding of black hole physics, but also galaxy evolution in general.

Feb. 17 Establishing the Empirical Relationship between Non-science Majoring Undergraduate Learners' Spatial Thinking Skills and Their Conceptual Astronomy Knowledge
Inge Heyer (Department of Physics and Astronomy, University of Wyoming)

In order to determine the relationship between students' spatial reasoning skills and their ability to learn astronomy content, 86 undergraduate students in a non-major introductory astronomy survey class were given astronomy knowledge diagnostics at the beginning and end of a semester-long introductory astronomy survey course, as well as spatial reasoning diagnostics in the middle of the semester. All data were matched. Spatial reasoning appears to be moderately to strongly related to astronomy knowledge. The correlation between astronomy post-course scores and spatial scores suggests that the relationship between spatial reasoning and astronomy ability explains about 25% of the variation in the data.

Mar. 2 The Formation of Galaxy Nuclei
Anil Seth (Department of Physics and Astronomy, University of Utah)

Compact, massive nuclear star clusters are found at the centers of most elliptical and spiral galaxies. They are among the densest stellar systems in the universe, and often coexist with massive black holes. The mass of both the black holes and nuclear star clusters correlates with the mass of their host galaxies, suggesting a link between the accretion of material into the central parsecs of a galaxy and its overall evolution. My work focuses on understanding this link and the connection between nuclear star clusters and black holes. I will present results on how galaxy nuclei acquire their mass using cutting-edge observations of the closest nuclear star clusters. These nearby nuclei also represent the best targets for dynamically detecting the lowest mass (<10^6 Msol) central black holes, which are key to understanding the initial formation of black holes in the early universe.

Mar. 23 What Drives the Growth of Black Holes?
Ryan Hickox (Department of Physics and Astronomy, Dartmouth College)

Supermassive black holes are amazingly exotic and yet ubiquitous objects, residing in the centers of essentially all stellar bulges in galaxies. Recent years have seen remarkable advances in our understanding of how these black holes form and grow over cosmic time, and how energy released by active galactic nuclei connects the growth of black holes to their host galaxies and large-scale structures. I will review a few recent observational and theoretical studies that explore AGN activity over a wide range of scales, from the inner accretion flow to the outer regions of galaxy clusters, and using a variety of techniques from observations of individual objects to simulations of whole cosmological volumes. Together, these studies are leading us toward a remarkably detailed picture of how black holes grow and influence their surroundings, and show that black holes have an important (and perhaps unexpected) role to play in history of the Universe.

Mar. 30 Debris Disks and the Epoch of Terrestrial Planet Formation
Christine Chen (Space Telescope Science Institute)

The terrestrial planets in our Solar System are believed to have formed via a multi-stage process that included the conglomeration of sub-micron sized interstellar dust particles into kilometer-sized parent bodies, the growth of pluto-size planetary embryos from collisions of kilometer-sized parent bodies, and the accretion of the patina from giant collisions between planetary embryos. The Spitzer Space Telescope has enabled photometric surveys of mid- and far-infrared excess around stars in nearby young associations that constrain models for the formation of pluto-sized objects, and spectroscopic characterization of the circumstellar material that suggests that giant collisions may be occurring in some systems. In this talk, I will outline the properties of young debris disks in which terrestrial planets may be forming, compare MIPS photometric observations of stars in the 5-20 Myr old Scorpius-Centaurus OB Association to the evolution predicted by self-stirred disk models, and discuss possible diagnostics for giant collisions in young Solar Systems.

Apr. 13 Merger-Induced Black Hole Accretion and Star Formation: Observations vs. Simulations
Hai Fu (Department of Physics and Astronomy, UC Irvine)

Galaxy mergers are inevitable in the mass assembly history of galaxies and their supermassive black holes. In merger simulations, gravitational torques induce rapid star formation and black hole accretion in both galaxies by driving gas deep into their nuclei. Such a phenomenon has been observed in a number of merging galaxies. However, it was unclear how well the simulations match the observations, quantitatively. I will talk about two experiments designed to address this issue. First, through a systematic search of kpc-scale binary active galactic nuclei, I will show that mergers enhance black hole accretion at a level consistent with simulations. Secondly, through detailed mid-IR spectroscopy of a complete sample of luminous infrared galaxies at z ~ 0.7, I will show that black hole accretion during intensive star formation allows merging galaxies to evolve along the fundamental scaling relation between galaxy mass and black hole mass.

Apr. 20 Bridging the Gap Between Mathematics and Physics
Tevian Dray (Oregon State University)

As with Britain and America, mathematicians are separated from other scientists by a common language. Students often have trouble "bridging the gap" between the presentation of mathematical concepts in mathematics courses and the use of those concepts in physics applications such as E&M. Casual discussions with faculty in other disciplines suggest far more agreement than exists in fact. In a nutshell, mathematics is about functions, but science is about physical quantities. This has far-reaching implications not only for the teaching of lower-division mathematics "service" courses, but also for the training of mathematicians.

For the last decade, I have led an NSF-supported effort to bridge this gap at the level of second-year calculus. The unifying theme we have discovered is to emphasize geometric reasoning, not (just) algebraic computation. In this talk, I will illustrate the language differences between mathematicians and physicists, and what this implies for the teaching of mathematics in general, and vector calculus in particular.
Apr. 20 Envisioning Upper-division Curriculum Reform
Corinne Manogue (Oregon State University)

You are thinking that your upper-division courses need more pizzazz, but revitalizing your curriculum seems intimidating. How do you modernize the content while maintaining the strengths of the traditional curriculum? What "hidden curriculum" issues do you need to address to prepare your students for the future? Can you balance the curricular needs of students bound for industry, graduate school, and other more interdisciplinary careers? Are the pedagogical strategies of lower-division reform appropriate to the upper-division?

The successful, NSF-funded Paradigms in Physics project at Oregon State University suggests answers to these questions, many of which are quick and easy to implement. Our project has involved both a rearrangement of content to better reflect the way professional physicists think about the field and also the use of a number of reform pedagogies which place responsibility for learning more firmly in the hands of the students. I will share some of our joyful experiences and hard-learned lessons.
May. 3 Soft Magnetic Thin Film Applications at Radio Frequencies
Prof. Masahiro Yamaguchi (Tohoku University)

Development of new passive component technologies will enable a "More-than-Moore" paradigm leading to innovative application-specific compact systems. Ferromagnetic thin film materials, having high permeability at (and above) radio frequencies, are candidate materials for use in inductive passive components that are available in the forms of vacuum-deposited and electro-deposited metallic alloys, chemically synthesized nano-particulate composites, and traditional oxides, among others. Using these materials, the development of CMOS integrated inductors and integrated electromagnetic noise suppressors for Long Term Evolution, or 3.9th Generation, cell phone RFIC and Point-of-Load one-chip DC-DC converters, is attracting great interest from both academic and industrial communities. This lecture begins with a review of new soft magnetic thin film applications at radio frequencies for future system-in-package (SiP) and system-on-chip (SoC) technologies. Proposed in late 1970s, these thin film soft magnet applications have evolved from inductive read/write recording head technology to the frontiers of GHz frequency device applications. Discussions covered in this lecture include: (1) Development of international cross measurements of RF permeameters to evaluate RF permeability and related FMR profiles of magnetic films; (2) small signal high permeable low loss applications to CMOS integrated inductors; (3) small signal lossy application to CMOS integrated electromagnetic noise suppressor; (4) small to medium signal applications as new metal/ferromagnetic multi-stack "conductors" to suppress skin effect utilizing negative permeability beyond the FMR frequency [ur' < 0, ur''=0]; and, (5) large current permeable application to Point-of-Load type one-chip DC-DC converters. The lecture will conclude with an outlook that provides a perspective on the future of on-chip RF magnetics.

June. 13 Title, TBC
Gerrit E.W. Bauer (Tohoku University)

Abstract, TBC

Previous colloquia series: Fall 2002 Spring 2003 Fall 2003 Spring 2004 Fall 2004 Spring 2005 Fall 2005 Spring 2006 Fall 2006 Spring 2007 Fall 2007 Spring 2008 2008-09 2009-10
Contact for program information: Adam Myers