| Date | Host | Speaker | Title of the talk | Abstract |
| Aug. 21 | Dubois | Antonio Carlos Fontes dos Santos,
Universidade Federal do Rio de Janeiro
Brasil | Ionization and Fragmentation of Molecules by ion and photon impact | Ionization
and fragmentation of molecules by charged particles or photons has many
applications in many scientific areas such as plasma physics,
astrophysics and upper planetary atmosphere physics. In this talk, we
present results on ionizing collisions of intermediate energy charged
particle impact and UV or soft X-rays photons with molecules. For the
photon impact case, a new and unexpected resonant-like structure was
observed in the fragmentation of water molecule, which is interpreted
as a dynamical electron correlation. |
| Aug. 28 | Yamilov | Gary Yao,
BioEngineering,
UMC | Optical Diffuse Reflectance in Skeletal Muscle | Normal
biomechanical and physiological functions of striated muscles are
facilitated by the repeating sarcomere units. Light scattering
technique has been used in studying single extracted muscle fibers.
However, few studies, if any have been conducted to investigate the
possibility of using optical detection to examine sarcomere structure
changes in whole muscles. We conducted a series of experiments to
demonstrate that the sarcomere structure plays a significant role in
modulating light propagation in whole muscle. The diffuse reflectance
patterns measured in whole muscle are related to changes in the
sarcomere structure. These results suggest that photon migration
technique has a potential for characterizing in vivo tissue
ultrastructure changes in whole muscle. |
| Sept. 4 | Yamilov | Maksim Skorobogatiy
Ecole Polytechnique de Montréal | Color-on-demand photonic textiles using plastic photonic bandgap fibers | We
present the fabrication and use of plastic Photonic Band Gap Bragg
fibers in photonic textiles for applications in interactive cloths,
sensing fabrics, signage and art. In their cross section Bragg fibers
feature periodic sequence of layers of two distinct plastics. Under
ambient illumination the fibers appear colored due to optical
interference in their microstructure. Additionally, Bragg fibers guide
light in the low refractive index core by photonic bandgap effect,
while emitting a portion of guided color without the need of mechanical
perturbations such as surface corrugation or microbending. Intensity of
side emission is controlled by varying the number of layers in the
Bragg reflector. Emitted color is very stable over time as it is
defined by the fiber geometry rather than by spectral content of a
light source. Moreover, Bragg fibres can be designed to reflect one
color when side illuminated, and to emit another color while
transmitting the light. By controlling the relative intensities of the
ambient and guided light the overall fibre color can be varied, thus
opening an opportunity for the passive color changing textiles.
Finally, we argue that all-plastic Bragg fibres offer economical
solution demanded by textile applications. |
| Sept. 11 | Waddill | Faculty presentations:
Research opportunities | Hagen
Yamilov
Vojta
Jentschura | |
| Sept. 18 | Wilemski | William Klein
Boston U | A Physicist's View of Earthquakes | Earthquakes
can cause considerable loss of life and property. Unlike hurricanes,
fires and floods, earthquakes strike with almost no warning. To
forecast earthquakes will require considerable insight into their
physics. Tantalizing clues lie in the fact that fault systems appear to
be operating near critical points. The evidence for a critical point is
in the appearance of scaling laws such as the Gutenburg-Richter power
law distribution of the number of earthquakes of magnitude m and the
Omori law for the number of aftershocks as a function of time. However,
there is also clustering of earthquake events and evidence of an
earthquake cycle in which large events cause a lessening of earthquake
activity until the system reloads the stress dissipated in the large
event.
In order to understand these processes we
have studied simple models of earthquake fault systems with some
surprising results. In this talk I will discuss the physical properties
of a certain class of models and the relation of these models to real
fault systems. The models indicate a mechanism that can produce both
scaling and an earthquake cycle and can be seen, in the right range of
parameters that control the physics, to be in the same universality
class as Ising models and simple fluids. |
| Sept. 25 | Waddill | Faculty presentations:
Research opportunities | Dubois
Parris
Medvedeva
Schulz | |
| Oct. 2 | Schulz
| Zaal Machavariani,
Tbilisi State University
| Single and double ionization of two electron atomic and molecular systems by charged particles impact | Single
ionization, double ionization and simultaneous ionization–excitation of
atoms and molecules by charged particles have been a subject of
intensive theoretical and experimental investigations during the last
decade. The reason is that the treatment of such four-body processes is
the effective tool for the studies of atomic electronic structure and
ionization mechanisms.
In my talk I will consider electron
impact double ionization (DI) of helium atom and proton impact single
ionization of hydrogen molecule. Both targets are two electron systems
and represent the unique samples for studying correlation effects as in
initial target state as well as in the final continuum state. As
concern DI of helium our approach is based on the possibility of
including in the consideration the angular correlation between the
target electrons, repulsion between the ejected electrons (in an
approximate way), and at the same time, to calculate the fully
differential cross section (FDCS) analytically. In order to calculate
total DI cross section this is an essential step forward which
facilitates the numerical calculation of TCS. Based on dynamical
variational principal the effective, momentum-dependent screened
charges have been calculated for both outgoing electrons. Hence, the
asymptotic behavior of the DI TCS has been explained.
Doubly
differential cross sections (DDCS) for single ionization of molecular
hydrogen by 75 keV proton impact have been calculated in the so called
one independent center approximation. In this approximation DDCS for
hydrogen molecule can be represented as twice corresponding atomic
cross section multiplied on some phase factor describing molecular
nature of the target. For qualitative explanation of the interference
structure observed in a scattering angular dependence of the DDCS the
projectile-target interaction has been taken into account for
calculation of independent atomic scattering cross sections.
|
| Oct. 9 | Dubois | Christian Buth, Louisiana State University | Atoms and molecules interacting with ultrafast x-ray lasers | X-ray
science is undergoing one of its greatest revolutions to date with the
construction of intense x-ray free electron lasers in Stanford, USA
(LCLS), Hamburg, Germany (XFEL), and Harima Science Garden City, Japan
(SCSS). These are vast, several-hundred-million dollar machines that
will provide x-ray pulses that are many million times brighter
than current sources. Similarly groundbreaking are the emerging
attosecond light sources based on intense, pulsed lasers; they are
relatively inexpensive laboratory-size instruments. These two emerging
radiation sources will enable radically new research and have
unnumbered potential applications in materials science, chemistry,
biology, AMO, condensed-matter, and plasma physics.
My work
contributes to a theoretical understanding of atoms and molecules in
gas phase which are exposed to light from these x rays and laser
sources. This lays the foundation for future studies using such new
resources. So far my work has been based on x rays from a
third-generation synchrotron facility synchronized to pulsed, intense,
optical lasers. Specifically, I discuss in my talk:
(i) How
laser-dressed atoms interact with x rays: the novel effect
electromagnetically induced transparency (EIT) for x
rays; provides opportunities for ultrafast x-ray pulse shaping.
(ii)
how laser-aligned molecules can be probed with x rays: properties
of laser-alignment of molecules; probing molecular dynamics with x
rays.
I will also give an outlook on proposed experiments on
double core holes in laser-aligned molecules at Stanford's LCLS and the
control of Auger decay on an electronic time scale using attosecond
light pulses. |
| Oct. 17 | Alexander | Homecoming:
Ray Vandiver
Oregon Museum of Science and Industry | | |
| Oct. 24 | Yamilov | MST&UMSL
meeting:
Fred Schlachter
Lawrence Berkeley National Laboratory
and
Americal Physical Society | Over a barrel: America’s energy crisis
| America’s
energy security and economic stability are in danger due to our
reliance on imported oil. We face the additional threat of global
climate change caused by combustion of fossil fuels. America has less
than 5% of the world’s population, yet we consume fully 25% of the
world’s energy. Reducing our energy consumption without changing our
quality of life will require political will, significant changes in our
use of energy, reducing our “carbon footprint,” and major improvements
in technology. We as scientists and engineers have a responsibility to
discover new cost-effective energy sources and means of reducing our
energy use. This talk will address the above issues and propose
research directions in science and technology. |
| Oct. 30 | Medvedeva | Renat Sabirianov
U of Nebraska, Omaha |
Novel effects in spin-dependent transport | Spin
dependent transport in a synergistic combination with novel nanoscale
magnetic and ferroelectric structures can be used to manipulate
spin-dependent currents yielding new paradigms for device operation. I
will discuss recent advances in spintronics concentrating on the
discovery of new magnetoresistive phenomena:
(1) ballistic
anisotropic magnetoresistance (BAMR) [1], a quantized change in the
ballistic conductance of the nanowires and nanocontact with
magnetization direction.
(2) voltage induced
magnetoresistance(MR) sign reversal.[4] Transition metal oxides
exhibit large changes in conductivity when an appropriate bias is
applied [2], which make them promising for memory devices [3]. The
change in the MR associated with this transition has not been, however,
explored, but may uncover fascinating physics. We have recently
observed a MR sign reversal associated with the bias dependent on/off
state in a Ni/NiO/CoNi/NiO/Co magnetic tunnel junction (MTJ) in
nanowire geometry at T=1.5K [4]. This behavior may be explained by a
metal-insulator transition driven by a charge accumulation controlled
by applied bias voltage.
[1] J. Velev, R. F. Sabirianov, S. S.
Jaswal and E. Y. Tsymbal, “Ballistic anisotropic magneto-resistance”,
Phys. Rev. Lett. 94, 127203 (1-4) (2005).
[2] G. Dearnaley, A. M.
Stoneham, and D. V. Morgan, “Electrical phenomena in oxide films”, Rep.
Prog. Phys. 33, 1129-1191 (1970).
[3] R. Waser, Nanoelectronics and Information Technology (Wiley, Weinheim, 2003).
[4]
A. Sokolov, R. Sabirianov, I. Sabirianov, and B. Doudin, “Resistive
switching of tunneling magnetoresistance in artificial nano-filaments”,
submitted paper. |
| Nov. 6 | Vojta | Michel Gingras
U of Waterloo | Geometric Frustration in Magnetic Pyrochlore Oxides |
Geometric frustration arises in a magnetic system whenever the
interacting magnetic moments cannot minize their total classical energy
by minimizing their pairwise magnetic interactions, pair by pair. The
pyrochlore oxides, of generic chemical formula R2M2O7 (R = Y, Gd, Tb,
Ho, Dy, Er, Yb; M = Mo, Mn, Ti, Sn), are highly prone to magnetic
frustration effects and have attracted wide theoretical and
experimental attention over the past fifteen years. In these systems,
both the trivalent rare-earth ions (R or yttrium) and the tretravalent
transition metal ions M reside on distinct interpenetrating
three-dimensional lattices of corner-sharing tetrahedra. It has become
standard practice in the field to simply refer to this lattice
structure as the pyrochlore lattice. The pyrochlore lattice leads to
extremely high level of geometric magnetic frustration when the
nearest-neighbor R-R or M-M exchange interaction between Heisenberg
spins is antiferromagnetic. Interestingly, in the case of extreme local
Ising anisotropy, as realized in Dy2Ti2O7 and Ho2Ti2O7, ferromagnetic
interactions are also frustrated, giving rise to a so-called (spin ice)
phenomenology analogous to the problem of entropic proton disorder in
common water ice. Because of the high level of frustration, the ground
state of magnetic pyrochlore oxides is highly sensitive to small
perturbations of the spin Hamiltonian beyond the nearest-neighbor
coupling. As a result, these materials exhibit a plethora of very
interesting thermodynamic and magnetic phenomena. Examples of
phenomenologies include long range order, spin glass, spin ice,
collective paramagnetism, anomalous Hall effect, persistent spin
dynamics, order by disorder, magnetization plateau, and seemingly
hidden order. In this talk, I will review some of the salient problems
associated with the collective thermodynamic and magnetic phenomena
offered by these fascinating materials. |
| Nov. 13 | Yamilov | Lev Deych
City U of New York | Whispering gallery modes in microspherical resonators:
coupling and
scattering | Whispering
gallery modes (WGM) are high-Q resonances arising in optical
microresonators such as microspheres or microdisks. In this talk I will
present a unified theoretical approach to description of evanescent
coupling between several resonators arranged in a linear chain and
Rayleigh scattering of WGMs due to an individual subwavelength scatterer. |
| Nov. 20 | Yamilov | Thomas Vojta | 2008 Nobel Prize in Physics: Spontaneous Broken Symmetry | This year's Nobel Prize in Physics was awarded jointly to Yoichiro Nambu for "for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics" and to Makoto Kobayashi and Toshihide Maskawa "for
the discovery of the origin of the broken symmetry which predicts the
existence of at least three families of quarks in nature". This
talk gives an elementary introduction into the physics of spontaneous
symmetry breaking, and its consequences for shaping the world as we know it. |
| Dec. 4 | Parris | Fifteenth Annual Laird D. Schearer Prize Colloquium | | |
| Dec. 11 | Yamilov | Ping Yu
UMC | Holographic Optical Coherence Imaging | |
