Physics Seminar

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.