Physics Seminar

Galaxy Clusters: Unraveling Astrophysics in Cosmic Laboratories

Speaker: Dr. Stephen Walker (NASA GSFC)
Location: OPB 237, 2:50pm
Abstract: Galaxy clusters are the largest gravitationally bound structures of the universe, consisting of hundreds or thousands of galaxies. The total masses of clusters are colossal, reaching up to and beyond a million billion times the mass of the sun. These clusters continue to grow and accrete matter from the surrounding cosmic web of gas produced by the Big Bang. When the infalling gas falls into their deep gravitational potential wells, it is shock heated to tens of millions of degrees, forming the intracluster medium, which begins to emit prodigiously in the X-ray band. At the forefront of our understanding of galaxy clusters is the Perseus cluster, which because of its closeness and large mass is the brightest cluster in the X-ray sky, providing us with an unprecedented view of cluster astrophysics. In this talk I will provide an overview of our latest understanding of the wide range of physical processes occurring in the Perseus cluster and other clusters, from the balance between gas cooling and feedback from its central supermassive black hole, to relic features in the intracluster medium produced by ancient collisions with smaller groups of galaxies, all the way out to the cluster outskirts where it is continuing to grow.

Atom-by-Atom Engineering of Oxide Thin Films and Nanocomposites via Molecular Beam Epitaxy

Speaker: Dr. Ryan Comes (Auburn)
Location: OPB 237, 2:50pm
Abstract: Complex oxides comprised of multiple positively charged metal cations exhibit a host of intriguing and useful properties for new technologies. Perovskite oxides with the chemical formula ABO3 and spinel oxides with the formula AB2O4 have some of the richest behavior. These materials may be metallic, semiconducting, or insulating, and exhibit ferroelectricity, with a built-in electric polarization, ferromagnetism, or superconductivity. This combination of properties in a single class of materials offers rich opportunities for engineering of unusual combinations of behavior through the design of multi-layer thin film materials. Through the use of molecular beam epitaxy (MBE), we are able to engineer these materials down to the atomic level so that interfaces between two different perovskites can be controlled to produce desirable properties. In this talk I will present two examples of this type of interfacial engineering, showing how we can design, model, and characterize these properties through a wide variety of techniques. I will discuss our work using interfacial termination in polar/non-polar heterojunctions and superlattices to engineer electric fields in these materials. Using in situ x-ray photoelectron spectroscopy (XPS) characterization of the LaFeO3/n-SrTiO3 junction with differing interfacial termination, we extract the valence and conduction band alignment between the materials and show that we can tune the electronic structure by interfacial engineering. In LaFeO3-NiFe2O4 nanocomposites, we show for the first time that MBE can be used to grow these vertically-aligned nanocomposites that are of interest for magnetic and catalytic applications. Using a combination of atom probe tomography and scanning transmission electron microscopy, we visualize the lateral interfaces down to the atomic level with sensitivity to the elemental composition in each phase. These results open up a wide range of new opportunities to design multilayer and nanostructured materials to achieve specific properties that cannot be found in the bulk.

Building a Galaxy Cluster: A Multi-Wavelength Approach to Understanding Cosmic Giants

Speaker: Dr. Thomas Connor (Carnegie Observatories)
Location: OPB 237, 2:50pm
Abstract: While the name "galaxy cluster" conjures images of a grouping of galaxies, these structures are more accurately considered as reservoirs of dark matter and gas, whose massive size and cosmic position make them the go-to destination for most of the matter in the universe. Because of this, the assembly history of galaxy clusters is complicated and ongoing, making it both easier and harder to describe than, e.g., star formation. In this talk, I will focus on two aspects of cluster assembly: the accretion of new gas reservoirs from filaments and the origin of the properties of the quiescent galaxy population. In the first case, detection of emission from the gaseous cosmic filaments has been a long-standing challenge for X-ray astronomy. Here, I will describe an ultra-deep Chandra observation of a nearby galaxy cluster, the potential filaments detected, and the deep optical followup campaign I led to confirm these detections. Then, I will discuss how deep cluster observations from the Cluster Lensing And Supernova survey with Hubble (CLASH) identify a distribution in the cluster galaxy population and what that entails about the growth of "galaxy clusters."

In Situ Temperature Sensing and Thermal Management of Lithium-ion Battery Cells

Speaker: Dr. Guangsheng Zhang (UAH)
Location: OPB 237, 2:50pm
Abstract: Lithium-ion (Li-ion) batteries have been widely used in consumer electronics, power tools and electric vehicles (EVs). However, great challenges still exist in their performance, durability and safety, all of which are related to temperatures. In situ temperature sensing and thermal management are powerful tools in understanding and addressing these challenges. In this presentation, I will talk about my previous work at Penn State on in situ diagnosis of Li-ion battery cells for mechanism understanding and a novel Self-Heating Li-ion Battery (SHLB) structure design for superior low-temperature performance. I will also report my latest work at UAH on a novel Slow-penetrating Small Sensing Nail (SNAIL) technique for in situ diagnosis of battery safety.

Ionization Mechanism and Gas Phase Abundances for Warm Ionized Gas in Quiescent Galaxies

Speaker: Dr. Renbin Yan (University of Kentucky)
Location: OPB 237, 2:50pm
Abstract: An accurate knowledge of all phases of the interstellar medium in non-star-forming, quiescent galaxies is critical for understanding how they prevent star formation from happening. The majority of these galaxies contain line-emitting warm ionized gas, for which the ionization mechanism has been puzzling us for decades. First found in the nuclear region of galaxies, termed as low ionization nuclear emission line regions (LINERs), they were thought to be associated with active galactic nuclei, with lots of supporting multiwavelength evidence. However, recent spatially-resolved spectroscopy data have challenged this idea. I will first explain the intensive debate about the association between LINERs and AGNs, then present direct gas temperature measurements that can help differentiate the two most popular mechanisms: shocks and photoionization. Surprisingly, I found neither models could explain all of the observed line ratios, nor can the combinations of them do. I will also demonstrate how we can measure the gas-phase abundance patterns in them despite the uncertainty about their ionization mechanisms.

Single, Multiple, Independent, and Dependent Scattering in Multi-Particle Groups: A First-Principles Perspective

Speaker: Dr. Michael Mishchenko (Goddard Institute of Space Studies)
Location: OPB 237, 2:50pm
Abstract:  The terms “single,” “multiple,” “dependent,” and “independent” scattering have been ubiquitous in the phenomenological discipline of light scattering by particulate media (such as clouds, aerosol layers, particulate surfaces, and oceanic hydrosols). Yet there is a wide range of ad hoc definitions of these terms many of which are vague and conceptually inconsequential. In this paper we perform a first-principles analysis of these terms based on the rigorous volume-integral-equation formulation of electromagnetic scattering. We argue that scattering by a multi-particle group can be called independent if certain optical observables for the entire group can be expressed in appropriate single-particle observables. Otherwise one deals with the dependent scattering regime. The prime (and perhaps the only) examples of independent scattering are scattering scenarios described by the first-order-scattering approximation and the first-principles radiative transfer theory. The same formalism is used to clarify the meaning of the term “multiple scattering” and expose its purely mathematical character.

Optical Scattering Theory

Speaker: Dr. Kirk Fuller (UAH)
Location: OPB 237, 2:50pm
Abstract:  Understanding the interaction of a homogeneous sphere with an electromagnetic plane wave is to electromagnetic scattering theory what the hydrogen atom is to quantum mechanics and spectroscopy. Each begins with a wave equation, expressed in spherical coordinates, and lays the groundwork for the study of more difficult problems.

This talk will outline a first-principles development of the complete mathematical description of scattering and absorption of polarized light by homogeneous spheres. The extension of the theory to nonspherical particles will then be discussed.

Attendees will be encouraged to be on the lookout for rainbows, halos, glories and any other optical phenomena that may be associated with the interaction of light with microstructures, and to invest in a pair of polarized sunglasses.

Building a Quantum Computer

Speaker: Dr. Barry Sanders (University of Calgary)
Location: OPB 237, 2:50pm
Abstract: Quantum computing is moving from concept to experimental proofs-of-principle and even to commercial products. Various types are considered such as universal quantum computers, quantum simulators and quantum annealers. Promising media include atoms, photons and solid state. I present a high-level overview of the current state-of-the-art and aspirations for building quantum computers.

Eavesdropping a Noisy Radio Channel by Manipulation of Photon Bunching Statistics -- Theory and Simulated Performance

Speaker: Dr. Richard Lieu (UAH Physics & Astronomy)
Location: OPB 237, 2:50pm
Abstract: TBA.

Revealing the Hidden AGN and their Connection to Galaxy Evolution using Extragalactic Surveys

Speaker: Dr. Chien-Ting Chen (NASA MSFC)
Location: OPB 237, 2:50pm
Abstract: A crucial yet unexpected piece of the puzzle of the general frameworks of galaxy evolution is supermassive black holes (SMBHs) in galactic centers. Despite the vast difference in physical sizes to their host galaxies, the well-established tight relation between the central SMBH and galaxy bulge properties implies that galaxy and SMBH might follow a similar cosmic evolutionary path. However, there are many observational challenges in finding direct evidence for this connection. I will discuss results of recent observational studies on several aspects of the SMBH-galaxy coevolution paradigm, including the connection between SMBH and different host galaxy properties, and how we can use extragalactic surveys to constrain the primordial SMBH seeding models.

Current Department Research

Speaker: Drs. Don Gregory, Seyed, Sadeghi, and Lingze Duan
Location: OPB 237, 2:50pm
Abstract: Short talks summarizing the current research in the department. Aimed at undergraduate and graduate students.

Current Department Research

Speaker: Drs. James Miller and Themis Chronis
Location: OPB 237, 2:50pm
Abstract: Short talks summarizing the current research in the department. Aimed at undergraduate and graduate students.

Current Department Research

Speaker: Drs. Max Bonamente, Richard Lieu, and Ming Sun
Location: OPB 237, 2:50pm
Abstract: Short talks summarizing the current research in the department. Aimed at undergraduate and graduate students.