UAH Physics Seminars

Colloquium: 24 November 2009, Tuesday, 2:30pm, OB 234

Wed, 18 Nov 2009 14:24:27 -0600

Interaction of turbulence with shock waves

The heliosphere is highly turbulent. The termination shock interacts with the ambient turbulent medium. I will present some results on solar wind velocity fluctuations, pickup ion driven instability, and modeling the interaction of turbulence with shock waves.

Xianzhi Ao
UAHuntsville

Colloquium: 10 November 2009, 2:30pm, OB 234

Tue, 10 Nov 2009 14:03:38 -0600

Radio Interferometry and High Frequency Radio Observations of Radio Galaxies

I will present an overview of the use of interferometric techniques in radio astronomy, the emission mechanisms that produce radio-waves in celestial objects, and a discussion of some of the objects visible in the radio universe. I will then present the results of a multi-frequency investigation of a radio source at the center of a cluster of galaxies and discuss the implications of these observations for our understanding of physical models of these radio sources.

Nazirah Jetha
UAHuntsville

Colloquium: 27 October 2009, 2:30pm, OB 234

Thu, 22 Oct 2009 09:54:40 -0500

Coherent nanophotoics: How to subdue optics of metallic nanoparticles via semiconductor quantum dots

One of the main reasons that currently noble metallic nanoparticles are at the center of significant attentions is the fact that they support surface plasmon resonances. These resonances are now the cornerstones of many applications, ranging from optical nanosensors, sub-wavelength optical waveguides, and nano-thermometers, to fundamental physics such as plasmonic control of emission of semiconductor nanostructures. Despite these, control of the optical properties of metallic nanoparticles is still rather an obscure field of research. This is mostly related to the ultra short relaxation times of plasmons, which make any attempt to control optics of metallic nanoparticles face significant challenges.

In this talk, I will review a novel technique that we have recently developed to optically control plasmons in metallic nanoparticles. This technique allows us to use a semiconductor quantum dot as a tool to make a metallic nanoparticle virtually transparent at the peak of its plasmonic absorption. This control of plasmons here requires interaction of a hybrid system consisting of a metallic nanoparticle and a quantum dot with an infrared laser. I will discuss how this process can be used to optically control heat dissipation rate in metallic nanoparticles, forming what we called “thermal electromagnetically induced transparency”.

Seyed Sadedhi
UAHuntsville, Department of Physics

Colloquium: 20 October 2009, 2:30pm, OB 234

Tue, 20 Oct 2009 11:49:24 -0500

Simulation of relativistic shocks and associated radiation from turbulent magnetic fields

Plasma instabilities excited in collisionless shocks are responsible for particle acceleration. We have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron–positron jet propagating into an unmagnetized electron–positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electron's transverse deflection behind the shock. The ``jitter'' radiation from deflected electrons in turbulent magnetic fields has different properties than synchrotron radiation, which is calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets in general, and supernova remnants. New spectra based on simulations will be presented.

Ken Nishikawa
NASA MSFC

Colloquium: 13 October 2009, 2:30pm, OB 234

Mon, 12 Oct 2009 13:59:53 -0500

Termination Shock Surfing

Voyager Observations of the heliospheric termination shock (TS) are presented along with a brief discussion of the current and past state of our knowledge of the heliospheric boundary region formed by the interaction of the Sun's solar wind with the local interstellar medium. Voyager 2 observations of the TS are used to construct a model which indicates that shock surfing can account for the 'missing' energy in the solar wind plasma downstream of the TS. (Time permitting) I will discuss our new idea for using the conservation laws for macroscopic conducting fluids (i.e. the conservation laws underlying MHD) to include the back-reaction of the shock surfing mechanism on the electromagnetic fields in a quasi-self-consistent fashion.
Ross Burrows
UAHuntsville

Special Seminar: 12 October 2009, 2:30pm, OB 234

Wed, 23 Sep 2009 14:22:05 -0500

Mathematica in the Classroom

Aaron Pollock
Wolfram Research

MS Thesis Defense: 7 October 2009, 8:30am, OB 234

Wed, 23 Sep 2009 14:19:34 -0500

Using Saturated Absorption Spectroscopy for Detuned Laser Locking

Mr. Charles "Shampoo" Schambeau
Department of Physics

Colloquium: 6 October 2009, 2:30pm, OB 234

Mon, 05 Oct 2009 15:01:04 -0500

Interferometer as an Imaging System

The primary function of an interferometer is to produce a set of rays normal to the ideal test surface. This is often aided by the presence of a null lens for aspheric mirrors. However, there is an important secondary function...imaging. In commercial systems there is always a control for imaging the test optic’s aperture. In laboratory practice what’s usually done is to simply obtain a sharp image of the mirror rim/edge. But we should ask ourselves how well an interferometer performs this imaging function. Are the design criteria between the two functions really compatible? In this presentation we provide an initial look into this question. We will do so in the context of the Fizeau interferometer since this type is currently the main industry workhorse. The test optic employed will be a parabolic mirror and also an off-axis component of that mirror, i.e. an OAP. A null lens will connect the aspheres to the Fizeau. Our chief investigative tool will be optical modeling. The code employed is Zemax. Joe Geary
UAHuntsville CAO

Colloquium: 29 September 2009, 2:30pm, OB 234

Wed, 23 Sep 2009 14:31:04 -0500

The Legacy of the Ulysses Mission

Steve Suess
NASA MSFC

Colloquium: 22 September 2009, 2:30pm, OB 234

Tue, 15 Sep 2009 10:13:52 -0500

The Acceleration of Charged Particles at Collisionless Shocks in Space and Astrophysics

The acceleration of charged particles to the highest energies ever measured (~10**20 eV ) occurs in Astrophysical settings. How this happen is still not fully understood. It is believed by many that the diffusive shock acceleration mechanisms is the key to this puzzle because it naturally produces a power law for the accelerated charged particle spectrum over a wide range of energies as observations show. However, radiation measurements from remote astrophysical shocks such as supernovae remnants can take us only so far in figuring out the details of shock acceleration since the radiation is produced by the shock accelerated particles and we do not see these particles directly. With the discovery of the termination shock around the Sun in the solar system plasma when the Voyager 1 and 2 space craft crossed it in 2004 and 2007, we have detailed direct measurements of charged particles accelerated by a large-scale collisionless shock and about the shock itself. We will discuss how the Voyager observations challenge us to come up with a more sophisticated model for charged particle shock acceleration at quasi-perpendicular shocks, which in some ways are not as well understood as at quasi-parallel shocks.

Jakobus A. le Roux, Dept. of Physics
UAHuntsville

Colloquium: 15 September 2009, 2:30pm, OB 234

Wed, 09 Sep 2009 10:28:46 -0500

Electron Kinetics in Gas Discharges

Gas discharges present an example of extremely non-equilibrium systems. This property comes from a large difference between the mass of electrons and the mass of atoms and molecules. Due to the great distinction of mass, the energy exchange in elastic collisions between electrons and gas molecules is inefficient, and the application of electric fields results in electron heating up to energies of a few eV (30,000K) comparable to ionization potential of atoms (with gas remaining at the room temperature). Low temperature plasmas (LTP) of gas discharges are characterized by low ionization degree of 10-6-10-3 and electron temperatures two orders of magnitude larger than gas temperatures. The electrons produce exotic chemical reactions not possible in equilibrium systems. These LTPs are widely used in many modern technologies including semiconductor manufacturing (etching and deposition of computer chips), lighting, plasma display panels, etc. We will present examples of electron kinetics in different plasma sources, describe intriguing physics of self-organization at the kinetic level for ionization waves (striations) in Direct Current discharges, and describe state-of-the-art modeling and simulation of electron kinetics in LTPs.

Dr. Vladimir Kolobov
UAHuntsville

Colloquium: 8 September 2009, 2:30pm, OB 234

Thu, 03 Sep 2009 14:20:42 -0500

Sun-Earth Connection: A Tale of Two Ends from a Personal Perspective

Our Sun, as a variable star, plays a dominant role in controlling the near-Earth space environment. It is constantly emitting highly ionized material mostly composed of protons and electrons (so-called "solar wind"), carrying solar magnetic field. Thus formed solar atmosphere, called corona, stretches all the way to the Earth and beyond. Its dynamic and magnetic interactions with near-Earth space generate various adverse effects, ranging from spacecraft malfunction in space to power outage on the ground, impacting various aspects of human activities. I will briefly describe such effects related to the emerging research area of space weather. Then I will report my contributions to this area on two topics. One is the extrapolation of the solar coronal magnetic field from magnetic field observations on the solar surface, especially that in a finite active region. The other is the quantitative characterization, from in-situ spacecraft data, of transient structures ejected from the Sun that are often responsible for causing disturbances in near-Earth environment. The effort of seeking physical and causal connections between the Sun and Earth will also be presented. Finally I will summarize and offer some outlook for future endeavors, especially in the context of further collaborations with solar physicists and support by observational facilities, within CSPAR.

Qiang Hu
UAHuntsville

Colloquium: 1 September 2009, 2:30pm, OB 234

Thu, 03 Sep 2009 14:19:46 -0500

Effects of an Intracavity Resonant Medium on an Optical Cavity

Optical cavities provide sensitive detection of rotation through the shift in the cavity resonance frequencies, resulting from the Sagnac effect. We investigated the use of the anomalous dispersion, asscioated with an absorption resonance from an intracavity medium, for increasing the frequency separation of the cavity modes. Using a simple Fabry-Perot resonator with an intracavity rubidium vapor cell, we experimentally demonstrated the increase in the cavity scale factor, and found it to be in good agreement with theory for our absorption resonance, with small deviations resulting from the multi-level nature of the Rb87 D2 transition. The widths of the cavity resonances, modified by the presence of the dispersive medium, did not grow as quickly as the scale factor, resulting in increased cavity sensitivity, a finding contrary to previous expectations. We also demonstrated that the ground state hyperfine structure of the Rb87 atom can be used to tune the cavity scale factor via the technique of optical hyperfine pumping.

Krishna Myneni
US Army RDECOM

Colloquium: 25 August 2009, 2:30pm, OB 234

Tue, 18 Aug 2009 14:36:57 -0500

The Structure of the Outer Heliosphere: Numerical Simulations vs. Spacecraft Observations

The outer heliosphere is the part of the solar wind (SW) which is determined by its interaction with the local interstellar medium (LISM). Since the LISM is partially ionized, charge exchange between atoms and ions plays a major role in the SW-LISM interaction. The topology of this interaction will be described as a function of the SW and LISM properties. The coupling of the interstellar and interplanetary magnetic fields (IMF and ISMF) at the heliospheric interface will be described. The importance of pick-up ions will be emphasized.

Several examples of numerical solution of the SW-LISM interaction problem will be given in the attempt to match them the observations performed by the Voyager 1 (V1) and Voyager 2 (V2) spacecraft. The combined effect of charge exchange and ISMF pressure on the heliospheric asymmetries will be analyzed. Observational constraints on the ISMF orientation will be addressed. I will also show the interaction of the heliospheric discontinuities with the SW perturbations. Special attention will be given to the heliospheric response to Sun’s rotation and 11-year period of solar activity.

Finally, I will describe a suite of numerical codes developed by our research group in CSPAR/Physics Department. This suite is capable of performing rather sophisticated, very high-resolution calculations of a variety of problems in space physics.

Nikolai V. Pogorelov
UAHuntsville

Colloquium: 21 April 2009, 2:30pm, OB 234

Wed, 01 Apr 2009 11:07:17 -0500

Design and Optimization of Nanostructured Optical Filters

Optical filters encompass a vast array of devices and structures for a wide variety of applications. Generally speaking, an optical filter is some structure that applies a designed amplitude and phase transform to an incident signal. Different classes of filters have vastly divergent characteristics, and one of the challenges in the optical design process is identifying the ideal filter for a given application and optimizing it to obtain a specific response. In particular, it is highly advantageous to obtain a filter that can be seamlessly integrated into an overall device package without requiring exotic fabrication steps, extremely sensitive alignments, or complicated conversions between optical and electrical signals.

This research explores three classes of nano-scale optical filters in an effort to obtain different types of dispersive response functions. First, dispersive waveguides are designed using a sub-wavelength periodic structure to transmit a single TE propagating mode with very high second order dispersion. Next, an innovative approach for decoupling waveguide trajectories from Bragg gratings is outlined and used to obtain a uniform second-order dispersion response while minimizing fabrication limitations. Finally, high Q-factor microcavities are coupled into axisymmetric pillar structures that offer extremely high group delay over very narrow transmission bandwidths.

While these three novel filters are quite diverse in their operation and target applications, they offer extremely compact structures given the magnitude of the dispersion or group delay they introduce to an incident signal. They are also designed and structured as to be formed on an optical wafer scale using standard integrated circuit fabrication techniques. A number of frequency-domain numerical simulation methods are developed to fully characterize and model each of the different filters. The complete filter response, which includes the dispersion and delay characteristics and optical coupling, is used to evaluate each filter design concept. However, due to the complex nature of the structure geometries and electromagnetic interactions, an iterative optimization approach is required to improve the structure designs and obtain a suitable response. To this end, a Particle Swarm Optimization algorithm is developed and applied to the simulated filter responses to generate optimal filter designs.

Jeremiah Brown
Grassmere Dynamics

Colloquium: 14 April 2009, 2:30pm, OB 234

Tue, 14 Apr 2009 08:07:45 -0500

Whister Wave Turbulence in Space Plasmas

Dastgeer Shaikh, UAHuntsville

Special Seminar: 3 April 2009, 2:30pm, OB 234

Mon, 23 Mar 2009 11:36:41 -0500

Morphology and dynamics of polymer nanocomposites

Dr. M Goswami, ORNL

Colloquium: 31 March 2009, 2:30pm, OB 234

Mon, 30 Mar 2009 11:02:10 -0500

Infrared Sources for Dynamic Radiometric Sensor Testing

The presentation will explore some of the challenges and performance issues encountered when using infrared semiconductor lasers and LEDs for dynamic radiometric sensor testing. A hybrid projection system combining the technologies of an emissive resistor array device and an optically scanned laser diode array projector (LDAP) will be discussed first. It will be shown that high apparent temperature (high radiance) simulations can most efficiently be produced by the luminescent infrared radiation emitted by semiconductor sources. Aspects of the ideal infrared source will be described along with research to develop new devices to fill these technology gaps in dynamic infrared sensor testing.

Dr. Tommy Cantey
AMRDEC

Colloquium: 24 March 2009, 2:30pm, OB 234

Mon, 23 Mar 2009 11:33:57 -0500

Fermi GBM Observations of Terrestrial Gamma Flashes

Dr. Michael Briggs
UAHuntsville

PhD Dissertation Defense: 11 March 2009, 10:00am, OB 234

Wed, 18 Feb 2009 10:22:40 -0600

Detection of Spatially Extended Sources in High Energy Astrophysics with Special Application to Lunar Occultation

Occultation is a technique that enables image reconstruction and source identification with a non-imaging detector. Such an approach is well suited for a future survey mission in nuclear astrophysics. In particular, the Lunar Occultation Technique (LOT) utilizes the Moon as an occulting object and is the basis of a new gamma-ray survey mission concept, the Lunar OCcultation Observer (LOCO). Techniques utilizing the LOT to detect spatially extended emission, such as emission from the Galactic plane or Galactic Center region, have been developed. Using knowledge of detector position in lunar orbit, combined with lunar ephemeris and relevant coordinate transformations, occultation time series can be used to reconstruct skymaps of these extended Galactic emissions. Monte-Carlo Markov Chains (MCMC), incorporating the Metropolis-Hastings algorithm for parametric model testing, form the basis of the technique. Performance of the imaging methodology, and its application to nuclear astrophysics will be presented.

Mr. Peter Jenke

Colloquium: 10 March 2009, 2:30pm, OB 234

Tue, 03 Mar 2009 08:28:09 -0600

RY Scuting Along: Studying a Messy Binary

A long time ago in a binary far, far away, one star was growing while another was shrinking. Even though this actually happened 6000 years ago, the light from these events in the RY Scuti binary is just getting to us. Right now we see one star dumping some of its mass onto its companion - active mass transfer and a messy transfer at that. I'll show you how we gleaned information about the two stars (such as masses) and determined that there is a 2000 A.U. double-ring nebula and a 1 A.U. circumbinary disk around the two stars, gas leaking from L2, and an accretion torus around the mass gainer. Eventually, one or both of these stars will go supernova.

Erika Grundstrom, Vanderbilt University

Colloquium: 3 March 2009, 2:30pm, OB 234

Tue, 03 Mar 2009 08:25:21 -0600

Characterizing the X-ray emitting plasmas in young stars

Young, low-mass stars are copious producers of X-ray emission indicative of magnetic activity in the plasmas of these stars. The trends seen in correlating X-ray parameters with stellar properties in main sequence stars do not follow for young stars. As a result, different physical mechanisms maybe driving the X-ray emission in young stars. I will present both imaging and spectroscopic data from the Chandra X-ray Observatory of various types of young stars at different evolutionary stages. Our results indicate unique characteristics of the X-ray emitting plasmas of these young stars.
S. Shukla, Vanderbilt University

MS Thesis Defense: 27 February 2009, 2:30pm, OB 234

Fri, 27 Feb 2009 11:17:06 -0600

Numerical modeling of alpha-particle deposition in a field reversed configuration

Mr. Nilesh Dhote

Colloquium: 24 February 2009, 2:30pm, OB 234

Fri, 20 Feb 2009 09:04:52 -0600

Exploration of the Saturn System by the Cassini/Composite Infrared Spectrometer (CIRS)

Dr. Mian Abbas
NASA MSFC

PhD Dissertation Defense: 25 February 2009, 10:00am, OB 234

Mon, 12 Jan 2009 14:26:00 -0600

Lunar Occultation Imaging in Nuclear Astrophysics: A New Paradigm for Future Investigations

Nuclear astrophysics (~20-10000 keV) is one of the last electromagnetic regimes without a sensitive all-sky survey, and hence has tremendous potential for future discoveries. A mission dedicated to such a survey will enable studies ranging from a survey of accreting black holes, to probing star formation rates by observing supernovae and novae, as well as investigating the underlying processes that power Active Galactic Nuclei. The Lunar Occultation Observer (LOCO) addresses these goals using the Lunar Occultation Technique (LOT), an innovative imaging approach to an all-sky survey. Occultation imaging eliminates the need for a pixellated, or high spatial resolution, detector. As a result, this technique is relatively simple to implement, maximizes active detector area, and is highly cost effective. This work characterizes the performance of the LOT in relation to the detection of astrophysical point sources. Sensitivity, position resolution, and issues of source confusion are all presented.

Mr. Mathew Orr

Special Seminar: 10 February, 3:30pm, NSSTC 2096

Mon, 09 Feb 2009 11:31:59 -0600

Simulations of galaxy cluster mergers and cosmology

M. Chatzikos
University of Virginia

Colloquium: 10 February, 2:30pm, OB 234

Mon, 02 Feb 2009 09:42:59 -0600

Cosmic-ray acceleration and magnetic field amplification at supernova remnant shocks

I will present the mechanism of particle acceleration at supernova remnant shock waves and the role the production of turbulent magnetic field by cosmic rays has on the process. The topic will be reviewed from the perspective of new observations in X- and gamma-ray bands. I will also show the recent results on the modeling of the magnetic field amplification in the vicinity of shocks with efficient particle acceleration and the implications these results have for the problem of the origin of high-energy cosmic rays.

J. Niemiec
Iowa State

Special Seminar: 5 February, 2:30pm, OB 234

Mon, 02 Feb 2009 09:38:55 -0600

Probing dynamical-dark energy with galaxy clusters

Observational evidence has been accumulated over the past two decades that points toward a "concordance" cosmological model. While this standard model rests on the basis of General Relativity, the large-scale dynamics of the Universe seems to be dominated today by some form of dark energy. Understanding the nature and evolution of this mysterious fluid is among the main quests for contemporary astrophysics, cosmology and particle physics. One of the most promising ways to reach this purpose is through the study of structure formation in the Universe, that is significantly influenced by dark energy. I will show how the spatial distribution of galaxy clusters, the most massive structures in the Universe, is affected by the presence of dark energy, with especial focus on the possible detection of this effect with future X-ray and Sunyaev-Zel'dovich surveys. I will also show that the abundance of galaxy clusters, probed through the strong gravitational lensing statistics, can validate particular dark energy models.

C. Fedeli, U. Bologna

Colloquium: 3 February 2009, 2:30pm, OB 234

Thu, 29 Jan 2009 10:27:59 -0600

Cosmological Tests Using X-ray Observations of Clusters of Galaxies

X-ray emission from massive clusters of galaxies offers two independent and complementary methods for studying cosmology. The first uses measurements of the ratio of gas to total mass in hot, dynamically relaxed clusters to provide a standard ruler, directly tracing the expansion of the Universe. This procedure produces constraints on dark energy and the mean dark matter density that are competitive with those from type Ia supernova studies. The second method uses measurements of the distribution and growth of cosmic structure observed through the cluster X-ray luminosity function. These studies place tight constraints on the amplitude of the density perturbation power spectrum and provide an independent probe of dark energy. The growth of structure is also potentially a powerful probe of modified gravity theories and inflation. I will review recent results from these experiments and describe the prospects for improvement in the future.

A. Mantz
Stanford University

Special Seminar: 30 January 2009, 3:45pm, OB 234

Thu, 29 Jan 2009 10:30:33 -0600

Philosophical Issues about Idealizations in Physics

N. Jones
UAHuntsville

Colloquium: 20 January 2009, 2:30pm, OB 234

Thu, 15 Jan 2009 09:52:54 -0600

Statistics in Football and Politics

The college football season has just wrapped up with the BCS National Championship game, and the new President is about to be inaugurated. We have developed statistical approaches to both of these disparate topics. First, I will discuss the Colley Matrix method for ranking college football teams. This method is used by the BCS as one of the six official computer rankings that help seed the National Championship game. The method is rooted in an old gambling formula due to Laplace and a straight-forward correction for "strength of schedule." I will then turn to a method developed by J. Richard Gott, III, and myself for predicting winners of Presidential elections. Here we apply median statistics state-by-state to form our best guess as to the final electoral returns. In 2004 and 2008, our method called the winner correctly and missed only 1 and 3 states, for a net 4 and 2 electoral votes, respectively.

Wes Colley
UAHuntsville

Colloquium: 13 January 2009, 2:30pm, OB 234

Fri, 09 Jan 2009 11:42:26 -0600

Effect of MeV Si Ion Bombardment on Thermoelectric Properties of Sequentially Deposited SiO2/AuxSiO2(1-x) Nanolayers

We prepared 50 periodic nano-layers of electro-cooling system consisting of SiO2/AuxSiO2(1_x) super lattice with Au layer deposited on both sides as metal contacts. The deposited multilayer films have a periodic structure consisting of alternating layers where each layer is 10 nm thick. The purpose of this research is to tailor the figure of merit of layered structures used as thermoelectric generators. The super lattices were then bombarded by 5 MeV Si ions at three different fluences to form nano-cluster structure. Rutherford backscattering spectrometry (RBS) was used to monitor the film thickness and stoichiometry before and after MeV bombardment. We measured the thermoelectric efficiency of the fabricated device before and after 5 MeV bombardments measuring the cross plane thermal conductivity by third harmonic method, measuring cross plane Seebeck coefficient, and measuring electrical conductivity using Van der Pauw method. As predicted the electronic energy deposited due to ionization by MeV Si beam in its track produces nano-scale structures which disrupt and confine phonon transmission therefore reducing thermal conductivity, increasing electron density of state so as to increase Seebeck coefficient, and electric conductivity, thus increasing figure of merit.

S. Boudak, Alabama A&M University

MS Thesis Defense: 12 December, OB 234, 10:00am

Mon, 08 Dec 2008 15:05:06 -0600

High-latitude Core Ion Properties during Northward Interplanetary Magnetic Field Conditions

This work studies the properties of upward ion flows inside the auroral ring of the polar cap in the southern hemisphere using multiple spacecraft. Inside auroral ring, upward ion flows defying gravity have long been identified. However, their causes are still presently unknown. Loranc et al (1991) first suggested that there might be a relationship between the interplanetary magnetic field and the upward ion flows. In a later study, Zeng (2004) also suggested that there may be a correlation between northward interplanetary magnetic fields and upward ion flows above the polar cap.

In this work, to examine the proposal by Loranc et al (1991) and Zeng (2004), a detailed case study is performed. Using the Thermal Ion Dynamics Instrument on the POLAR satellite and the Defense Meteorological Satellite Program satellites 11, 12, 13, and 14, individual upward ion flows are identified and measured. Together with interplanetary magnetic field as measured by the WIND satellite, a correlation studies is performed.

To ensue our dataset is reliable, strict selection criteria are imposed; incidents of very low density were excluded; periods when the satellites were not flying over the polar cap within a minimum time range were also excluded. This leads to a clean dataset. Our analyses suggest that a northward interplanetary magnetic field is likely the primary cause of an upward ion flow in the polar cap. However, the upward ion flow pattern is complicated and varies from event to event.

Ms. Shannon Smith

Colloquium: 18 November 2008, 2;30pm, OB 234

Mon, 17 Nov 2008 08:24:14 -0600

Global Modeling of Heliospheric Processes: Achievements and Challenges

An overview will be presented of magnetic-field-related effects in the solar wind (SW) interaction with the local interstellar medium (LISM), as well as different theoretical approaches for their analysis. The effects to be discussed include heliospheric asymmetries caused by the interstellar magnetic field (ISMF), energy exchange between charged and neutral particles, stability of the heliopause, 11-year cycle of solar activity, the tilt of the heliospheric current sheet caused by the misalignment of the Sun's magnetic-dipole and rotation axes, propagation of large-scale perturbations, the possibility of a strong ISMF, etc. Numerical results are discussed in the context of their relevance to observational data. A package of computer codes capable of analyzing sophisticated flows of partially ionized plasma is described.

Nikolai V. Pogorelov
UAHuntsville

Colloquium: 11 November 2008, 2:30pm, OB 234

Thu, 06 Nov 2008 09:39:47 -0600

Exploring the Extreme Ends of the Gamma-Ray Burst Spectrum

Gamma-ray bursts (GRBs) are extreme phenomena: they are the brightest photon emitting events in the Universe, caused by a collimated ultra-relativistic flow, emerging from the deep potential well of a collapsed object. They are observed across the whole electromagnetic spectrum, spanning almost 16 decades in observing frequency. Multi-wavelength observations of GRBs and their so-called afterglows are used to study the physics of these extreme explosions, their progenitors and their surroundings. In this talk I will focus on the two extreme ends of the GRB spectrum: the prompt high-energy gamma-ray emission, in particular the latest results obtained with the Fermi Gamma-ray Space Telescope (launched in June); and the low-frequency radio emission, which for a small number of GRBs can be observed for years after the initial burst and provides unique information to constrain the physical models.

Alexander van der Horst,
NASA/MSFC

Colloquium: 4 November 2008, 2:30pm, OB 234

Mon, 03 Nov 2008 08:32:01 -0600

Black body test on the WMAP 5-year data

Pivotal evidence for the Big Bang origin of the cosmic microwave background (CMB) is its black body spectrum. The COBE FIRAS observation constrained any distortion in the all-sky CMB spectrum from the black body shape to 50 parts per million. By means of WMAP 5-year data, here we statistically compared among three well separated frequency passbands ~10,000 angular temperature fluctuations on the one degree scale. We find that on average the frequency dependence of the temperature is about 3 micro-K, or one part per million since T~ 3 K, thereby tightening the COBE constraint on the CMB spectral shape by another 50 times. Unlike COBE also, the residual dT represents the detection of a random component, or non black body signal. Further, a similarly small temporal variation is revealed by comparing spot temperatures at a fixed frequency but in different times. These extra fluctuations may contain important new physics about the early Universe.

B.Z. "Ally" Jiang , graduate student at Tsinghua University

Colloquium: 28 October 2008, 2:30pm, OB 234

Mon, 27 Oct 2008 09:38:14 -0500

The Acceleration of Solar Energetic Particles by Coronal Mass Ejection Driven Shocks

Fast coronal mass ejections (CMEs) in the solar corona drive interplanetary shocks that accelerate solar energetic particles (SEPs) to produce high levels of radiation near Earth that can be hazardous to astronauts and even passengers in high altitude spacecraft, damage satellites, and cause polar lights (aurora). However, the details of the shock acceleration process is currently not well understood. To model this process requires understanding of how energetic charged particles propagate in the largely collisionless solar wind plasma emanating from Sun. These basic propagation mechanisms will be reviewed and it will be showed that they can be combined into a single kinetic transport equation, the so called focused transport equation. This equation has supplanted the standard cosmic-ray transport equation in recent years as the best way to model SEP acceleration at CME shocks. It will be discussed how this equation contains the basic physics of collisionless shock acceleration. Numerical solutions of this equation will be shown to contrast the basic features of the acceleration and transport of SEPs for strong and weak CME shocks which differ substantially from the standard steady-state shock acceleration picture.

Jakobus A. le Roux
UAHuntsville, Department of Physics and CSPAR

Colloquium: 21 October 2008, 2:30pm, OB 234

Tue, 21 Oct 2008 11:03:12 -0500

The Heliospheric Termination Shock

Observations of the heliospheric termination shock (2007) reveal that the shock is similar in many respects to the structure expected for quasi-perpendicular shocks. However, the dissipation mechanism is fundamentally different and the thermal plasma downstream of the shock is unexpectedly cool. Nonetheless, the basic physics can be understood on the basis a theoretical model developed in 1996 by Zank et al. The observations and simple models will be discussed.

Gary Zank
UAHuntsville, Department of Physics & CSPAR

Special Public Lecture: 20 Oct 2008, 7:30pm, Davidson Center at the Space and Rocket Center

Tue, 14 Oct 2008 10:52:41 -0500

With amazing intuition, Einstein developed his theory of general relativity and published it in 1916. His equations predicted that space-time is warped by mass in the universe. They had an unexpected solution with a gravitational singularity from which even light could not escape - later named a "black hole" by John Wheeler. Others predicted that massive stars could, in principle, collapse to such a state. With the space age, X-ray telescopes found strong evidence that black holes really exist and are important components of the cosmos. Their birth is observed as fiery gamma-ray bursts. Still unproven are some of the more exotic predictions such as worm holes connecting distant parts of the universe and the evaporation of primordial black holes proposed by Stephen Hawking. This lecture will discuss all of the real and speculative aspects of black holes and return to the still-open question of "what is a black hole".

Neil Gehrels
NASA/Goddard Space Flight Center

Colloquium: 14 Oct 2008, 2:30pm, OB 234

Mon, 13 Oct 2008 09:36:42 -0500

Anomalous cosmic ray acceleration and the Voyager paradox

Anomalous cosmic rays (ACRs) are charged particles (ions and electrons) accelerated to high energies in the outer heliosphere, at distances of 80-150 AU from the Sun. The two Voyager deep space probes have been monitoring ACR activity for over 30 years. Starting in 2002 Voyager 1 began to observe a new, lower-energy particle population believed to the related to ACRs. This population became more intense as the spacecraft was approaching the solar-wind termination shock, long though to be the source of ACRs. However, as Voyager 1 crossed the shock near the end of 2004, energetic particle spectra did not unfold into a power law, as was predicted by theories of shock acceleration. Instead, the two-component nature of the spectrum persisted some distance into the heliosheath, the region of shocked solar wind acting as a "buffer zone" between the solar and the interstellar plasmas.

Voyager 2 observations made during its crossing in mid-2007 painted a similar picture, with a few quantitative differences. Several new theories have been put forward to explain the ACR paradox. As an enormous evolving structure with a complex shape and history the termination shock is unlike most interplanetary shocks in that particle acceleration occurs intermittently and only at some locations. For example, acceleration may be more efficient near the ecliptic plane or in the "flanks" of the shocks, both regions not visited by either Voyager. Shock acceleration is also heavily influenced by the dynamics of the solar wind whereby large-scale transient structures disrupt the acceleration process.

This talk will discuss competing new theories of ACR acceleration at a blunt and dynamically evolving termination shock in light of the recent Voyager results.

Vladimir Florinski
Department of Physics, UAHuntsville

Colloquium: 7 Oct 2008, 2:30pm, OB 234

Wed, 01 Oct 2008 09:09:26 -0500

The intermittent solar wind: current sheets and their role in energetic particle transport

In past years, measurements of the solar wind plasma have advanced our understanding of MHD turbulence tremendously. At small scales, the solar wind is believed to be very multifractal with nonlinear interactions causing an intermittent energy dissipation, leading to possible current-sheet structures. In this talk, I describe a novel data analysis procedure which allows us to both examine the existence and identify the location of current sheets in the solar wind. The presence of these structures introduces a new source of solar wind turbulence intermittency and can affect the transport of energetic particles.

Previous studies of energetic-particle transport in the solar wind often assume a uniform large-scale background magnetic field, with a turbulent field superposed. With the existence of current sheets in the solar wind, this picture needs to be changed. By constructing a model turbulence of the solar wind that includes explicitly flux-tube-like structures, we show that large scale perpendicular diffusion can come out without introducing a 2D geometry for the underlying MHD turbulence. The implications of this finding is discussed.

Gang Li
Physics, UAHuntsville

Colloquium: 30 Sept 2008, 2:30pm, OB 234

Tue, 30 Sep 2008 11:54:57 -0500

Pushing the Limits in Laser Physics: Design of Inversionless Lasers with Negative Threshold Gain

No Abstract.

Seyed Sadeghi
UAHuntsville

Colloquium: 23 Sept 2008, 2:30pm, OB 249

Tue, 23 Sep 2008 12:50:01 -0500

Overview of Medical Physics Practice and Research

No abstract.

Dr. Rob Rice
Clearview Cancer Institute

Colloquium: 16 Sept 2008, 2:30pm, OB 234

Tue, 23 Sep 2008 12:47:39 -0500

Following last semester's special video seminar on nanophotonics, I'm going to play the second part of the documentary DVD, which features two presentations on the recent development on some of the hottest topics in optics. These presentations were given by the topical group chairs of the Optical Society of America in last year's Frontier in Optics Conference. The first presentation reviews a number of new results in the area of quantum electronics, while the second focuses on two recent experiments on human vision and color. This seminar is intended to give students with all background an opportunity to peek into the cutting-edge research in the field of optical sciences. Again, I will give a brief tutorial on some of the subjects covered in the presentations, including attosecond optics, optical cloaking and quantum communications.

Dr. Lingze Duan
Physics, UAHuntsville

Colloquium: 9 Sept 2008, 2:30pm, OB 234

Tue, 09 Sep 2008 08:30:12 -0500

Nonlinear Processes in the the Solar Wind Plasma

No abstract.

Dr. Dastgeer Shaihk
UAHuntsville

Colloquium: 2 Sept 2008, 2:30pm, OB 234

Tue, 09 Sep 2008 08:29:49 -0500

The Dust - Plasma Thruster: A new concept in space propulsion

A new scheme of micro propulsion in space i.e. the dust - plasma thruster is proposed. The scheme uses plasma thermal energy to charge externally injected sub micron sized particles and simultaneously create electric fields in the plasma which accelerates them. Particles are subsequently charge stripped and exhausted to produce electrically neutral thrust obviating the need of a charge neutralizer. For reasonable plasma and particle parameters, thrust 10 - 50 micro-N and specific impulse 50-100 s may be produced. The scheme is shown to have modest power requirements. It may be realized in a simple design where there are no high voltage grids or electrodes, charge neutralizer, valves, pressurized gases etc and can operate in space or vacuum. A layout for the possible configuration is described.

Dr. Khare Avinash
UAHuntsville

Special Seminar: Thursday, 29 May 2008, 2:15pm, OB 234

Mon, 05 May 2008 10:08:02 -0500

Particle acceleration and transport in the inner heliosphere

Energization and transport of charged particles in the inner heliosphere has been a long standing problem in space plasma physics. At 1 AU, solar energetic particles (SEPs) with energies upto ~ 1 GeV arrive routinely. They interact with the Earth's magnetosphere, cause communication disruptions, pose radiation threats to spacecraft and astronauts, and are the main subject of NASA's space weather study. At least for one class of the solar energetic particle events, the so-called gradual SEP events, it is believed that the acceleration of particles is via shock acceleration at CME-driven shocks. As a CME-driven shock propagates out, particles are picked up at the shock front, accelerated through 1st-order Fermi-acceleration mechanism. Upstream of the shock, particles are capable of escape. When they do, they generate and amplify upstream Alfven waves, further enhance the subsequent acceleration process; leading to an integrated system with self-consistent particle acceleration and wave generation. Escaped particles propagate in the inner heliosphere following the Parker's spiral, with pitch angle scatterings. Pitch angle scattering describes the effect of turbulent magnetic field on charged particles and is a continuous stochastic process. Obviously, to decipher the observed time intensity profile and spectra at 1 AU for gradual SEP events, a detailed model treating shock propagation, particle acceleration, and particle transport is necessary. In this talk, I will discuss particle acceleration and transport in the inner heliosphere, putting into the context of the PATH (Particle Acceleration and Transport in the inner Heliosphere) model that I have been working in the past several years.

Dr. Gang Li obtained his Ph.D in nuclear astrophysics and Master in computer science from Indiana University in October 2000. His thesis work was on neutrino transport in Supernova and he won the outstanding graduate research award from Physics Department. He joined IGPP at University of California at Riverside as a post-doc late 2001 and became an professional researcher in 2004. In February 2006, he took a Assistant research physicist position in Space Science Lab at University of California, Berkeley. In his spare time, he loves hiking and playing badminton. Since February 2008, the arrival of his son, Luke, however, took all his spare time away.

Dr. Gang Li
UC Riverside

Special Seminar: Tuesday, 27 May 2008, 2:15 pm, OB 234

Mon, 05 May 2008 09:47:18 -0500

Cosmic ray interaction with plasma flows in the heliosphere

Cosmic rays comprise several ubiquitous particle populations in the solar system. Galactic cosmic rays are highly energetic particles originating from outside the solar system that serve as probes of magnetic fields and turbulence inside the heliosphere, while anomalous cosmic rays, being of heliospheric origin, offer unique insights into the physics of charged particle acceleration at highly oblique astrophysical shocks. The outstanding problem of modern cosmic-ray physics is understanding the interaction of these energetic particles with the global structure of the heliosphere. A number of heliospheric cosmic-ray transport models have been developed over the past 7 years at the UC Riverside to study in detail the interaction of cosmic rays with turbulent plasma flows in and around the solar system. Two principal applications of our models are discussed: (a) galactic cosmic-ray modulation in the heliosheath and (b) the response of anomalous cosmic rays to the variability of the termination shock induced by transient structures in the solar wind. My results suggest that the heliosheath is responsible for over half of the total modulation of cosmic rays with energies below 500 MeV, in agreement with Voyager observations. I also argue that the unexpected deficiency in the anomalous cosmic rays fluxes discovered by the Voyagers is a consequence of dynamical evolution of the termination shock.

Vladimir Florinski received his MS in Physics from the St. Petersburg State Technical University in St. Petersburg, Russia, in 1997. He did his PhD research on galactic and anomalous cosmic ray transport under the guidance of J. R. Jokipii at the University of Arizona. His PhD in Planetary Science was awarded in 2001. After graduation, Florinski worked as a postdoctoral researcher for G. P. Zank at the University of California in Riverside, where he is currently a Professional Researcher. Florinski is an author of over 50 publications and a co-organizer of several international astrophysics conferences. His principal research area is theoretical modeling of the full range of physical phenomena occurring in the outer heliosphere.

Dr. Vladimir Florinski
UC Riverside

Special Seminar: Thursday, 22 May 2008, 2:15pm, OB 234

Fri, 09 May 2008 09:20:56 -0500

MHD-neutral Model of the Outer Heliosphere

I describe the model of the solar wind (SW) interaction with the local interstellar medium (LISM) which takes into account the coupling of the interstellar and interplanetary magnetic fields (ISMF and IMF) at the heliospheric interface, charge exchange/collisions between ions and atoms, and time-dependent phenomena. The asymmetry of the heliosphere under the combined action of the interstellar magnetic field and charge exchange is analyzed. The solutions are shown for different ISMF orientations. The possibility is discussed of using the SOHO SWAN data on the deflection of neutral hydrogen flow from its original orientation in the unperturbed LISM as an ISMF compass. The effects of the solar cycle and SW transients are discussed. A newly developed package of scientific programs is described which was developed for solution of multi-scale space physics and astrophysics problems involving flows of charged and neutral particles that require gas dynamic, MHD, and kinetic treatment. The results are presented of the package application to numerical modeling of the outer heliosphere, in particular, to the problem of stability of the heliopause and heliospheric current sheet behavior.

Nikolai V Pogorelov
Institute of Geophysics and Planetary Physics
University of California, Riverside

Special Seminar: Monday, 19 May 2008, 2:15pm, OB 234

Mon, 05 May 2008 10:20:18 -0500

New Insights into Interstellar Pickup Ion Acceleration at the Heliospheric Termination Shock and in the Heliosheath

For many years prior to the discovery of the heliospheric termination shock (HTS) by the Voyager spacecraft, many anomalous cosmic-ray modulation effects observed upstream of the HTS could be explained satisfactorily by using the standard cosmic-ray transport equation to model the steady-state diffusive shock acceleration (DSA) of anomalous cosmic rays at the HTS. However, the first Voyager HTS crossings during 2004 and 2007 showed that energetic ion observations at the HTS cannot be easily explained within the confines of standard steady state DSA theory which is based on the assumption of energetic particles with nearly isotropic distributions. Observations such as upstream magnetic field-aligned energetic ion beams with large pitch-angle anisotropies that are highly volatile, an unexpected high energy peak in the upstream pitch-angle anisotropy, a large highly anisotropic intensity spike at the HTS, energetic ions with multiple power law spectral slopes, and spectral slopes that are harder than expected from steady state DSA theory, require a more sophisticated approach to DSA that is time dependent and is not restricted to small anisotropies. I will show that these observations can potentially be explained when modeling the DSA of pickup ions at the HTS with a time-dependent focused transport model. Secondly, first observations of the termination shock structure by the Voyager 2 spacecraft clearly suggest that the HTS is modified by accelerated pickup ions on macroscopic as well as microscopic spatial scales. This indicates that reflection and heating of pickup ions rather than solar wind ions by the cross-shock potential is important and that DSA at the HTS is a nonlinear process. I will discuss a promising self-consistent kinetic-three-fluid model that we developed that promises to give a good account of these observations. Thirdly, strong compressive turbulence is currently observed in the turbulent heliosheath. This begs the question whether turbulent diffusion and stochastic acceleration by compressive turbulence in the heliosheath could explain observations that suggest that HTS accelerated pickup ions are further accelerated to higher energies in the heliosheath. I will discuss this possibility based on theoretical work we did on energetic ion transport and energization in compressive wave turbulence.

Dr. Jakobus le Roux
UC Riverside

Special Seminar: Thursday, 15 May 2008, 2:15pm, OB 234

Mon, 05 May 2008 10:13:22 -0500

Turbulence in Interstellar Medium Plasma: A Coupled Plasma-neutral Fluid Model in the Heliosphere

A local turbulence model is developed to study energy cascades in the interstellar medium (ISM) based on self-consistent two-dimensional fluid simulations. The model describes a partially ionized magnetofluid interstellar medium (ISM) that couples a neutral hydrogen fluid with a plasma primarily through charge exchange interactions. Charge exchange interactions are ubiquitous in warm ISM plasma and the strength of the interaction depends largely on the relative speed between the plasma and the neutral fluid. Unlike small length-scale linear collisional dissipation in a single fluid, charge exchange processes introduce channels that can be effective on a variety of length-scales that depend on the neutral and plasma densities, temperature, relative velocities, charge exchange cross section and the characteristic length scales. We find, from scaling arguments and nonlinear coupled fluid simulations, that charge exchange interactions modify spectral transfer associated with large scale energy containing eddies. Consequently, the warm ISM turbulent cascade rate prolongs spectral transfer amongst inertial range turbulent modes. Turbulent spectra associated with the neutral and plasma ISM fluids are therefore steeper than those predicted by Kolmogorov's phenomenology. This work has important implications for the nature of the interstellar medium, especially in understanding heating characteristics, cosmic ray transport, interstellar medium processing by a partially ionized plasma, and molecular clouds and star formation processes where ion-neutral interaction influence magnetic fields.

Dr. Dastgeer Shaikh
UC Riverside

Special Seminar: Monday, 12 May 2008, 2:15pm, OB 234

Mon, 05 May 2008 09:46:03 -0500

Seeing the heliosphere through energetic neutral atoms

The interaction of the solar wind with the partially ionized plasma of the local interstellar cloud is investigated. We introduce the concept of the heliosphere as a bubble of solar wind embedded in the local interstellar medium. With the help of 2D and 3D numerical simulations, we investigate the effects of interstellar neutral hydrogen on the heliosphere, and various approaches to modeling neutral atoms will be discussed. These neutral atoms are coupled to the plasma through charge-exchange, but since the mean free path is of the order of the heliosphere itself, the coupling has a variety of non-local features. We then look at observational implications of neutral atoms in the heliosphere, in particular for the upcoming IBEX mission. We show, by using data from our simulations, how all-sky maps of energetic neutral atoms (ENA's), born through charge-exchange in the heliosheath, can yield information about the structure of the heliosphere. It is envisioned that IBEX data will help to constrain models of the heliosphere and thereby improve our understanding of the farthest reaches of the Sun's environment.

Undergrad and grad studies at the University of Waikato in New Zealand, graduated in 2001. Held a temporary position as assistant professor at the same place. Worked mainly on solutions to the MHD equations to describe magnetic reconnection. Came to Riverside in 2003 as Post-doc. Promoted to assistant professional researcher in 2004. Developed a Monte-Carlo code which kinetically models hydrogen atoms in the heliosphere and coupled this to an MHD code for the ionized plasma.
Dr. Jacob Heerikhuisen
UC Riverside

Colloquium: 22 April 2008, 2:30pm, OB 234

Wed, 23 Apr 2008 11:41:51 -0500

Ex Luna, Scientia!

The Lunar Occultation Observer (LOCO) is a new mission concept being developed to probe the nuclear astrophysics regime.By combining the development heritage of planetary orbital-geochemistry investigations with new developments in astrophysical imaging, a high-sensitivity, scaleable, and cost effective mission is feasible. LOCO will perform an all-sky survey of the Cosmos and study a wide range of astrophysical phenomena including, but not limited to, Galactic nucleosynthesis, supernovae & novae, potential dark matter annihilation processes, active galactic nuclei, and compact objects. I will describe the motivating science, the mission concept, as well as ongoing research and development.

Dr. Richard Miller
UAH

Colloquium: 15 April 2008, 2:30pm, OB 234

Mon, 07 Apr 2008 16:04:28 -0500

Nanophotonics: From Photonic Crystals to Plasmonics

In this special seminar, I’m going to play a documentary DVD, which shows a plenary presentation given by Professor Eli Yablonovitch of UC Berkeley at the Frontiers in Optics Conference last September. Dr. Yablonovitch is widely regarded as the father of photonic crystals. In this beautifully organized talk, he took the audience on a tour of structures far smaller than the wavelength of light and reviewed the latest progress in three of today’s hottest areas in optics: photonic crystals, silicon photonics and plasmonics. When the size of integrated circuits dropped below the critical dimension for a photonic crystal, which is about 100 nm, electronics and optics have become one thing. With the breakthrough of silicon lasers, a full toolkit for integrated optoeletronics is at hand. Finally, the emerging field of plasmonics will eventually make possible integrated optical circuits.

To help students with limited optics background better understand the talk, I’m going to give a brief tutorial of some of the background knowledge before the presentation. This will be a good opportunity for students to get a taste of conference and learn about the latest development in the field from a world-class expert.

Dr. Lingze Duan
UAH Physics

Colloquium: 8 April 2008

Mon, 31 Mar 2008 14:02:28 -0500

No talk today. UAH Honors Day.

Colloquium: 1 April 2008, 2:30pm, OB 234

Mon, 24 Mar 2008 08:36:06 -0500

The Polar Ultraviolet Imager (UVI): A Dozen Years of Auroral Science

The Polar satellite, originally scheduled for a two-year mission, recently celebrated its twelve-year anniversary of operations. The Ultraviolet Imager (UVI), one of three imagers on Polar, is a camera designed to view Earth’s aurora in ultraviolet wavelengths. That remarkable mission is now drawing to a close and the Polar satellite is scheduled to be shut down by the end of the month. This presentation is intended to be a celebration of the UVI investigation and, more importantly, a tribute to the UAH-MSFC collaboration that designed, built, tested and operated the instrument. UVI images allow scientists to monitor the location and behavior of the aurora, determine auroral energies and properties of Earth’s upper atmosphere. Advantages of space-based imaging of the aurora and imaging of the upper atmosphere in general will be discussed. Results will be presented from UVI and form other global imagers before and after the Polar era.

Dr. Glynn Germany, UAH/CSPAR

Colloquium: 25 March 2008, 2:30pm, OB 234

Mon, 24 Mar 2008 08:31:27 -0500

The FUSE Survey of Diffuse O VI Emission from the Interstellar Medium

Emission via the O VI doublet at 1031.93 and 1037.62 A is the primary cooling mechanism for interstellar gas at temperatures between 10^5 and 10^6 K. As such, it traces regions where hot gas cools quiescently, interface regions where hot and cool gas meet and mingle, and high-velocity shocks. Over its eight-year mission, the Far Ultraviolet Spectroscopic Explorer (FUSE) was used to observe O VI in both emission and absorption. In this talk, I will present a brief history of the hot component of the interstellar medium (ISM) and the various physical processes responsible for its creation, evolution, and morphology. I will review the results of recent O VI absorption- line studies of the Galactic disk and halo. Finally, I will present the latest results from our survey of diffuse O VI emission from the ISM.

Our observations reveal the large-scale structure of the O VI-emitting gas in the quadrant of the sky centered on the Magellanic Clouds. Its most prominent feature is a layer of low-velocity emission that extends more than 70 degrees from the Galactic plane. By combining absorption and emission measurements along the same lines of sight, we can estimate the emission measure and therefore the density of the emitting gas. We identify two distinct populations of emitting clouds: At low latitudes (|b| <30 deg), we probe narrow, high-
density conductive interfaces in the local ISM. At high latitudes, the low densities and long path lengths are consistent with a location in the Galactic thick disk/halo. Three of our sight lines exhibit O VI emission at velocities consistent with Magellanic H I, suggesting that hot and cool gas is mixing in the interface region of the Magellanic System.

Dr. Van Dixon
Johns Hopkins University Dr. Van Dixon
Johns Hopkins University

Colloquium: 18 March 2008

Thu, 13 Mar 2008 08:17:37 -0500

None. Spring Break.

Colloquium: 11 March 2008, 2:30pm, OB 234

Thu, 13 Mar 2008 08:14:55 -0500

Understanding Cometary Atmospheres

Understanding the chemical and physical properties of cometary atmospheres is crucial to understanding comets as a whole. However, many properties of cometary atmospheres are still not understood. This is further compounded by the lack of models incorporating information gathered from comet flyby missions. I will discuss my recent and ongoing work to examine the potential impact of gas dynamics, photochemistry, and chemical reactions on the chemical profiles of cometary atmospheres, including an attempt to model chemical profiles in the atmosphere surrounding a non-spherical nucleus. The results have implications for measuring chemical abundances in comets, and in turn, measuring chemical abundances in the outer Solar System and placing constraints on scenarios of Solar System formation.

Dr. Donna Pierce
Mississippi State University

Colloquium: 4 March 2008, 2:30pm, OB 234

Mon, 25 Feb 2008 15:49:03 -0600

Measuring the Magnetic Field in the Solar Corona

The corona is the outermost layer of the Sun's atmosphere. Remarkably, it has a temperature of 1-2 million degrees Kelvin, while the layers of gases in the photosphere only a few thousand kilometers below (which we see as the disk of the Sun) have a temperature of about 6000 K. The structure of the corona is partly determined by a magnetic field, as may be seen in pictures of solar eclipses. This magnetic field is widely believed to play a role in the heating of the corona, either directly via Joule heating or indirectly via the damping of waves and turbulence which involve the magnetic field. Assessing this role requires measurements of the strength and structure of the coronal magnetic field. I will describe ways in which such information can be obtained by radioastronomical measurements. The physical effect at the basis of these measurements is Faraday Rotation, consisting of a rotation of the plane of polarization of a radio wave when it propagates through an ionized gas with a magnetic field.

Dr. Steve Spangler
University of Iowa

Colloquium: 26 Feb 2008, 2:30pm, OB 234

Wed, 20 Feb 2008 14:06:20 -0600

Electric Redshift and Quasars

Recently, a new redshift mechanism called electric redshift is developed by Zhang (ApJL 636, 61, 2006), in accord with the five-dimensional fully covariant Kaluza-Klein (K-K) theory with a scalar field, which unifies the four-dimensional Einsteinian general theory of relativity and the Maxwellian electromagnetic theory. The result indicated that a dense, massive, and charged object can significantly shift the light that is emitted from the object toward the red as compared with the Einsteinian gravitational redshift. A compact, electrically charged object with density and mass comparable to those of a neutron star can impart a redshift as great as quasars have. This seminar introduces this new redshift mechanism and discusses the detectability of the electric redshift and the scalar field interaction with possible experiments.

Dr. T. X. Zhang
Alabama A&M University

Colloquium: 19 Feb 2008, 2:30pm, OB 234

Thu, 14 Feb 2008 13:47:35 -0600

Relativistic MHD Simulations of Relativistic Jets

Relativistic jets have been observed or postulated in various astrophysical sources, including active galactic nuclei (AGNs), microquasars in the galaxy and gamma-ray bursts (GRBs). There are four major problems related to the relativistic jets: 1. formation mechanism, 2. acceleration mechanism, 3. collimation mechanism, and 4. long-term stability. The most promising mechanisms for producing and accelerating relativistic jets, and maintaining collimated structure of relativistic jets involve magnetohydrodynamical processes.

We perform 2D general relativistic MHD simulations involving a geometrically thin accretion disk near both non-rotating and rotating black holes by using newly-developed 3D GRMHD code ``RAISHIN''. In the rotating black hole case an inner jet forms near the black hole region in the magnetic field strongly twisted by frame-dragging. This inner jet/spine lies within an outer jet/sheath produced by the magnetic fields anchored accretion disk. When the jet propagates, such a jet/spine and sheath/wind configuration considerably modifies the stability properties and potential structure of the jet resulting from spine-sheath interaction. We have performed 3D relativistic MHD simulations to study the Kelvin-Helmholtz (KH) instability of magnetized spine-sheath relativistic jets. We found that the growth of the KH instability is reduced significantly by a mildly relativistic sheath flow and can be stabilized by a magnetized sheath flow.

Dr. Y. Mizuno
MSFC/NSSTC

PhD Dissertation Talk: 20 Feb 2008, 2:30pm, OB 234

Mon, 11 Feb 2008 11:36:10 -0600

Vaporization and Shock Wave Dynamics for Impulse Generation in Laser Propulsion

A high-power carbon dioxide laser was used to ablate bulk liquid, polymer, and thin film targets. Time-resolved force sensing measurements, ballistic pendulum impulse measurements, and quantitative shadowgraph and Schlieren imaging techniques were used to study ablation. Propulsion parameters (including imparted impulse, momentum coupling coefficient, ablated mass, specific impulse, and internal efficiency) were measured for the materials when possible. In addition, a detailed examination was conducted as to the dependence of these parameters on the absorption depth of the materials, and on the fluence at the target. An initial study was made on the scaling of the propulsion parameters with the ablated spot area. The effects of varying the thin film thickness on the impulse were also noted. A calibration technique for piezoelectric force sensors was developed using impacts of spheres on the sensors. Finally, a basic physical analysis of the propulsive quantities was made that raises questions about the standard interpretation of the dependence of the coupling coefficient on the fluence.

Mr. John Sinko
UAH Physics

Colloquium: 12 Feb 2008, 2:30pm, OB 234

Fri, 08 Feb 2008 20:55:59 -0600

Quantitative Detection of Proteins Using an Evanescent Based Fiber-Optic Biosensor

In recent years, there is a considerable increase in the research efforts in the field of fiber-optic biosensors. Because of their potential sensitivity, detection speed and adaptability to a wide variety of assay conditions, their use as a probe or as a sensing element is increasing in clinical, pharmaceutical, industrial and military applications. I will talk about design aspects of a fiber-optic probe and converting it into a highly sensitive and specific tool for rapid and cost-effective detection and quantification of proteins in serum/plasma samples.

Dr. R. Kapoor
UAB

Colloquium: 5 Feb 2008, 2:30pm, OB 234

Mon, 04 Feb 2008 09:47:33 -0600

Experimental Studies of Charging of Lunar Dust: Levitation, Adhesion, & Transportation

It is well known since the Apollo missions that the lunar surface is covered with a thick layer of micron size dust grains with unusually high adhesive characteristics. The dust grains levitated and transported on the lunar surface are believed to have a hazardous impact on the robotic and human missions to the Moon. A horizon glow and transient dust clouds over the lunar horizon were observed by during the Apollo 17 mission. The observed dust phenomena are attributed to the lunar dust being charged positively during the day by UV photoelectric emissions, and negatively during the night by the solar wind electrons. The dust grains are believed to be levitated by the induced electric fields and transported in the near vacuum environment. The current dust charging and the levitation models, however, do not fully explain the observed phenomena, with the uncertainty of dust charging processes and the equilibrium potentials of the individual dust grains. Since the abundance of dust on the Moon's surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies.

It is well recognized that the charging properties of individual dust grains are substantially different from those determined from measurements made on bulk materials that are currently available. An experimental facility has been developed in the Dusty Plasma Laboratory at NASA Marshall Space Flight Center for investigating the charging and optical properties of individual micron/sub-micron size dust grains by levitating them in an electrodynamic balance in simulated space environments. I will discuss our recent results on laboratory measurements on charging of Apollo 11 and 17 individual lunar dust grains by low energy electron beams and by photoelectric emissions. The measurements are made by levitating dust grains of 0.2 to 10 mm diameters, in an electrodynamic balance and exposing them to mono-energetic electron beams and UV radiation. The charging rates and the equilibrium potentials produced by UV radiation and by electron impact are discussed. Photoelectric emission induced by the solar UV radiation is recognized to be the dominant process for charging of the lunar dust. In a unique laboratory facility at MSFC/NSSTC, the optical and physical properties of individual lunar dust grains are being investigated with the objective to better understand the complex lunar dust phenomena in order to develop and evaluate various mitigating strategies. We will discuss the first laboratory measurements of the photoelectric yields of individual sub-micron/micron size dust grains selected from sample returns of Apollo 17, and Luna 24 missions, as well as similar size dust grains from the JSC-1 simulants. The measured yields of micron-size individual dust grains are determined to be more than an order of magnitude larger than the bulk values reported in the literature, with a size dependence that indicates higher values for larger grains. The current and future experimental and analytical programs for investigations of the lunar dust phenomena will be discussed.

Dr. Mian Abbas
NASA MSFC

Special Seminar: 31 Jan 2008, 2:30pm, OB 234

Mon, 28 Jan 2008 08:32:34 -0600

Ultra-High-Energy Cosmic Rays: New Results from the Auger Array

The highest energy cosmic ray particles are the most energetic particles known to us in the universe, and their observations have led us to build one of the largest detector system in the world, the Auger air-shower array. We have detected particles of an energy up to 3x10^20 eV, which is a macroscopic energy. There have been two predictions: one that due to interaction with the microwave background the spectrum should show a turnoff near 5x10^19 eV; this has been confirmed by two experiments, HiRes and Auger. Second, that radio galaxies should be the accelerators, based on the non-thermal optical spectra of knots and hot spots in radio galaxies; this is now tentatively confirmed by Auger. Apart from differentiating various remaining options how to generate these particles, there is one major difficulty: the lack of understanding of the cosmological web of magnetic fields, which may influence the propagation of high energy particles; here it is especially important to understand the role of a galactic wind and its magnetic structure. In analogy to the scattering of particles in the Solar wind I propose, that this scattering leads to a steep distribution function of scattering angles of the deviation from a straight line path for the arriving particles. I will discuss the observational and theoretical limits for an exemplary set of models, the predictions, that result from these models, and how present and future observations will test our conclusions, especially with the Telecope Array (TA), the Auger Array, the neutrino observatory IceCube, and the future space observatory EUSO. There are a number of exciting consequences for high energy physics.

Dr. Peter Biermann
Max Planck Institute (Bonn)

Colloquium: 29 Jan 2008, 2:30pm, OB 234

Wed, 23 Jan 2008 08:37:13 -0600

Heliophysics Science and the Moon

The Moon is immersed in a plasma environment - the local cosmos - that is "magnetized." It is threaded with magnetic fields that are often "frozen" into the plasma, a state of high electrical conductivity that effectively couples the motions of the plasma and the magnetic field. This inherently strong coupling means that the structure and evolution of magnetic fields (of the Sun, of the Earth, and even of the Moon itself) play an essential role in organizing and regulating the local environment of the Moon - the environment to be experienced by explorers. By working to understand, and so predict, the variations that occur from day to day, and from region to region, the productivity and overall success of future lunar robotic and manned missions can be significantly enhanced. This talk will articulate some of the viable investigations that can be pursued at the Moon that address topics of Solar and Space Physics. The content is based on a community based report in press entitled "Heliophysics Science and the Moon"

Dr. James Spann
NASA MSFC

Special Seminar: 18 Jan 2008, 10:30am, NSSTC 2096

Wed, 23 Jan 2008 08:37:33 -0600

Chandra/ACIS Observations of Massive Star Forming Regions

Much of the stellar populations inside of the massive star forming regions are poorly studied in the optical and infrared wavelengths because of observational challenges caused by large distance, high extinction, and heavy contamination from unrelated sources. High spatial resolution X-ray images have opened a new window to probe the rich intermediate-mass and low-mass young stellar populations accompanying the massive OB stars in each region. I present Chandra/ACIS observations of two massive star forming complexes, namely the NGC 6357 region and the Rosette Complex, concentrating on the new census of low-mass cluster members and new knowledge of the IMFs. These studies demonstrate the unique power of studying star formation in the X-ray band.

Dr. Junfeng Wang
Penn State

Colloquium: 15 Jan 2008, 2:30pm, OB 234

Wed, 23 Jan 2008 08:37:51 -0600

The Multi-Universe Cosmos - A New cosmological theory of the birth of the cosmos, our universe, and its fate

I propose an entirely new approach to the origin of the Cosmos and our universe, one of many in a Multi-Universe Cosmos. The new model eliminates the mysterious singularity at time 0, the origin of which and its explosion no one can explain. It is the first theory which describes the creation of the Universe using laws of physics which hold everywhere and embody the conservation law of energy. Long before any universe was born, the 4-dimensional cosmic space-time was created and all laws of physics established.

Karel Velan
Velan, Inc

Colloquium: 8 Jan 2008, 2:30pm, OB 234

Wed, 23 Jan 2008 08:38:20 -0600

Physics and Astrophysics from the Gamma-ray Large Area Space Telescope (GLAST)

GLAST is a major space observatory planned for launch by NASA in May 2008. It will explore the GeV gamma ray region of the cosmic gamma ray spectrum with fifty times the effective sensitivity of previous facilities and help investigate gamma ray bursts. It is expected to make major discoveries involving black holes, neutron stars, cosmic rays and the sun. In addition, it has the capability to detect a signal from annihilating dark matter.

Roger Blandford
Kavli Institute, Stanford University