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Graduate Student Seminar Series,
2005-2006 |
Conceptual change is a common theme in science education.
Much work has been devoted to uncovering students' conceptions and documenting
the changing process of learning science. Built upon the existing literature,
this study examines the intellectual resources of studying conceptual change
from historical, philosophical and psychological perspectives; selects a
history of research in conceptual change in the past three decades; and
proposes a new theory of conceptual change focused on modeling.
Observations of Ultra-Heavy galactic cosmic rays (GCR) help
to distinguish the possible origins of GCRs. The Trans-Iron Galactic Recorder
(TIGER) is designed to measure the charge (Z) and energy of GCRs using a
combination of scintillation counters, Cherenkov counters, and a scintillating
fiber hodoscope. TIGER has accumulated data on two successful flights from
McMurdo, Antarctica: the first launched in December of 2001 with a total flight
duration of 31.8 days and the second in December of 2003 with a total flight
duration of 18 days. The final analysis of the combined data of these flights will
someday yield a PhD for me and another graduate student seminar to boot. I will
present the current status of this analysis. In order to have something more
substantive to talk about I will describe the analysis I carried out for the
solar particle event (SPE) TIGER detected on December 26, 2001 at 5:30 UT
during its first flight from McMurdo Base in Antarctica. Preliminary analysis
of the data from this event presented at the 27th ICRC indicated the possible
detection of heavy Solar particles (Si to Fe) from above 600MeV/nuc to
~GeV/nuc. TIGER was not designed for the particle flux seen during the SPE, and
the analysis I will present addressed the problems of reduced particle track
assignment efficiency and reduced charge resolution due to the high flux
identified in the preliminary analysis. I will show that my results indicate
that there was no elevation of the heavy particle flux during the SPE. I will
of course show the obligatory TIGER pictures, and I will reminisce about
TIGER's prehistory.
One way to study nuclear structure far from stability is by
doing experiments in which the unstable nuclei are created via fusion-evaporation
reactions. The nuclei are produced at excited energy states and decay by
emitting alpha particles, protons, neutrons, and gamma rays. By detecting the
emitted particles, one can determine the identity of the "daughter"
nuclei and study the paths they take to de-excite to a lowest energy (ground)
state. Various models which interpret these decay paths are then used to give
us a picture of the properties of the nucleus, such as its shape and modes of
motion of its constituent protons and neutrons. Recently an experiment was
performed at Argonne National Laboratory to study the nucleus 92Pd. This
nucleus is produced with very low cross section, and is thus extremely
difficult to detect. In my talk I will explain how one goes about "catching"
such a rare nucleus and studying its properties.
Galaxy clusters may be sources of TeV gammma-rays emitted
by high-energy photons and electrons accelerated by large scale structure
formation shocks, galactic winds of cluster active galactic nuclei.
Furthermore, gamma-rays may be produced in dark matter particle annihilation
processes at the cluster core. First, I'll describe the technique we use to
observe TeV gamma-rays and discuss what it's like to work in the high-energy
astrophysics group here at Washington University. Then, I'll report on
observations of the galaxy clusters Perseus and Abell 2029 using the 10 m
Whipple gamma-ray telescope during the 2003-2004 and 2004-2005 observing
season.
The short term goal of my project is to successfully make
amorphous thin films of an AlYFeTi alloy. Along the way we decided to study the
morphology of the films as a function of temperature and deposition rate. To
better understand this system i studied the average particle size, number
density and area coverage. That's the boring stuff. The really fun is that i
get to shoot metals with lasers, freeze Si waffers with Liquid nitrogen and
etch through my samples with 48% hydroflouric acid. All in a day's work!
The talk provides an introduction to variational
perturbation theory (VPT), which converts divergent weak-coupling series into
exponentially fast convergent strong-coupling expansions. In order to perform
the resummation, one introduces artificial variational parameters whose
influence is then optimized according to the principle of minimal sensitivity.
As an introductory example, the ground-state energy of the quantum-mechanical
anharmonic oscillator is considered. Examples for the successful application of
VPT are given. Subsequently, a D-dimensional anharmonic oscillator is examined.
It is demonstrated how the large-D expansion for its ground-state energy can be
extracted by using VPT.
In order to reduce the world's consumption of fossil fuels,
an important scientific goal is the discovery of viable alternative energy
sources. One popular possibility is the hydrogen fuel cell. The focus of this
talk is to review current methods being undertaken here at Wash U to explore a
quasicrystalline alloy, Ti/Zr/Ni, as one such viable source. Recent results
will be compared against the standards put forth by the US Department of Energy.
There will also be a short discussion of theoretical questions and the other
merits of hydrogen storage to basic science.
Cells stably expressing the EGF receptor fused with EGFP
were studied using fluorescence correlation spectroscopy and fluorescent
brightness analysis. A new approach was developed to quantify the degree of
clustering of the receptors on the cell surface, based on an analysis of
brightness. Unexpectedly, disruption of lipid rafts by cholesterol depletion
enhanced EGF receptor clustering. A new interpretation of the effects of
cholesterol depletion on the association of EGF receptors with lipid rafts is
presented which is consistent with these novel observations.
After introducing the fundamentals of Nuclear Magnetic
Resonance in a helpful but largely painless manner, I will discuss my work with
gallium nitride. We'll address the applications of this fantastic compound, its
future hopes and plans, and what one can learn about it using NMR. I should
likely also mention the unique predicted and observed properties of amorphous
and thin-film GaN. Afterwards, we will retire for dinner and dancing.
High-pressure experiments are an invaluable tool for
understanding matter in the condensed state. In particular, the application of pressure
allows one to drastically vary sample parameters to an extent that would not be
possible using other means such as chemical substitution. In this talk I will
outline the history of high-pressure experiments and explain how high pressure
experiments led to the discovery of the first superconductors suitable for
practical applications. I will present some of our group's results on
superconducting elements under extreme compression (approaching 1 million times
atmospheric pressure). Finally, I will discuss some of the bizarre predictions
(including room-temperature superconductivity) for high-pressure phases of the
simplest and most abundant element, hydrogen.
While numerous studies have focused on the effects of
altered relaxation or stiffness on early rapid filling, the concept of
diastolic filling efficiency incorporating relaxation parameters has not been
derived or validated. Previous studies showed that quantitative determination
of relaxation parameters can be achieved by assessment of early rapid filling
(Doppler E-wave) via kinematic modeling. E-wave kinematics is governed by
harmonic oscillatory motion, modeled via the parameterized diastolic filling
(PDF) formalism. Kinematic diastolic filling efficiency can be derived using
this formalism. In this presentation, I will talk about basic physiology, then
introduce efficiency concept in a physical way, derive an filling efficiency
index and validate the index using diabetic cardiomyopathy as an example. It
will be fun.
Perception is strongly visually oriented, so a detailed
examination of the organizational principles involved in the reception and
processing of visual information in the brain is very important. We have
started to uncover the synaptic, dendritic, and network mechanisms of
spatiotemporal information processing underlying the computation of visual
motion. Based on our experimental data and computer simulation we show that at
least two mechanisms are involved in the processing of visual information
provided by the retina to the optic tectum of birds.
We are interested in analyzing high density and low
temperature QCD. This can best be done in the cores of neutron stars. I have
been calculating several observational quantities of neutron stars for
different possible phases of matter inside the star. Hopefully, these
quantities will be different enough to provide a distinguishing characteristic
to say that one of these phases of matter is favored and therefore provide us
with a diagnostic/experimental tool for the underlying microscopic physics.
The strong force binds quarks into hadrons and nucleons
into nuclei. In principle, quantum chromodynamics (QCD) describes all strong
interaction phenomena, from the mass spectrum of hadrons to nuclear fusion. In
practice, the breakdown of perturbation theory makes calculating even the mass
of the nucleon a major theoretical and computational challenge. Beginning with
an overview of the Standard Model and current searches for new physics, we will
qualitatively examine the techniques of non-perturbative field theory as
applied to extracting the hadron spectrum and consider the role that these
methods have to play in the search for new physics.
The random, amorphous structure of glasses yields these
materials significant strength and toughness over those materials with the
weaknesses of crystal defects and grain boundaries. When such structure is
combined with the workability and durability of metals, one can produce a
metallic glass - a unique class of materials whose strong yet elastic
properties allow for remarkably effective applications from golf clubs to
surgical instruments. However, arriving at the exact alloy composition and
processing steps that can yield a metallic glass requires a careful balance of
geometric, chemical, and thermodynamic influences, along with great patience.
In this talk, I will outline what is know of the physical basis of this unique
state of matter and discuss my current work to produce an aluminum-based bulk
metallic glass.
It has been widely reported that glass formation improves
in Zr_62 Cu_20 Ni_8 Al_10 alloys when small amounts of Ti are substituted for
Zr. Glasses containing greater than 3 at.% Ti crystallize to a metastable
icosahedral phase, suggesting that Ti enhances icosahedral short range order in
the liquid/glass, making crystallization more difficult during cooling. Based
on /in-situ/ high-energy synchrotron diffraction studies of electrostatically
levitated supercooled liquids and rapidly quenched amorphous alloys,
icosahedral short range order was confirmed by a distinct shoulder on the
high-q side of the second peak in S(q). In practice, with containerless
solidification and x-ray diffraction studies of these alloys, we demonstrate
that Ti inhibits surface crystallization but neither increases the icosahedral
short-range order nor improves glass formation.
Last year, an extraordinary optoconductance (EOC) of 500%
at 30K was announced in a gallium arsinide (GaAs) indium hybrid structures. At
room temperature, though, the EOC drops to negative 10%. Recent attempts to
optimize the EOC have shown a room temperature effect of 50% in InSb hybrids. A
drift diffusion model using finite element modeling reproduces the temperature,
current, and positional dependence of the voltage. The emergent science in our
lab include a new extraordinary effect. A room temperature extraordinary
electroconductance (EEC) of 200% was realized in GaAs hybrid structures. Next,
X-ray studies reveal the effect of transfer printing on pentacene structure.
Finally, a theoretical calculation in delta doped quantum well heterostructure
of the product of carrier concentration and mobility shows how the composition
influences sensor parameters. This has implications in the design of optimal
EXX devices.
When a gymnast does a handstand, blood flows from their
venous reserves into the active circulation, and the heart must take in that
extra blood during filling. Importantly, only the total volume handled by the
heart changes and the actual filling ability of the heart stays the same.
However, if a cardiologist used modern techniques to measure the gymnast's
heart function during the headstand and compared that to his heart function
during upright standing, the measurement would show that both volume and
function changed. This is because currently, intrinsic heart filling function
and extrinsic volume load cannot be effectively uncoupled when measurements of
heart function are made. This represents a serious problem in the assessment of
heart function, and has remained and unsolved problem for 30 years. In our lab
we use physics to model how the heart fills. This allows for more quantitative
assessment of heart function, provides solutions to unanswered problems in
cardiology, and leads to new predictions about cardiovascular physiology. In
this talk I provide a quantitative method to uncouple the effects of volume
load and intrinsic filling function, thereby solving the "Load Independent
Index of Filling Problem.
Our group uses an approximation of general relativity
called the post-Newtonian approximation. I will give a brief overview of this
approximation and then talk about my project, which is to show that the second
post-Newtonian order is free of so called self-energy terms, in accordance with
the strong equivalence principle.
So, you ask, "What in the world does
"Boingy-Boingy-Boingy-..." mean?!" -Could it be a ball bouncing around?
-Could it be three troublesome cartoon characters wreaking havoc upon all they
touch? -Could it mean that I have lost my mind? -Could it be the most basic
physical characterization of one of your organs? Well, of course the answer is
yes to all of those questions! But this week, I'm only going to discuss the
last one. Here's a quick synopsis: When your heart (okay, fine you nit pickers,
your left ventricle) finishes pushing blood into your arteries, it starts to
reduce its pressure and fill via the following equation: d2x/dt2+c*dx/dt+k*x=0
That's right, the heart is no harder to solve than a (mass normalized) damped
harmonic oscillator. So to hear more about the heart, and find out the answer
to these questions: -Will I be kidnapped or mortally wounded before I get to
talk, bringing an ignominious end to the year for Vic and Chris? -Will the
oscillator equation be the only one I put in my talk? -Will I succeed in
putting in more pictures in my talk than words? -Will I have found my sanity
before Friday afternoon? Come to Grad Seminar!