A Portable Water Cherenkov Detector: Measuring Particle Flux at Different Altitudes. LUKAS BAUMGARTEL (University
of New Mexico, Albuquerque, NM, 87131) BRENDA DINGUS (Los Alamos National Laboratory, Los
Alamos, NM, 87545)
High-energy cosmic
particles initiate extensive air showers (EAS) as they interact
with the air molecules in Earth’s upper atmosphere. If the primary
particle carries sufficient energy, the shower reaches the ground.
With an array of photo-multiplier tubes (PMT’s) located in a pool
of water, the direction and energy of the primary particle can
be reconstructed from the Cherenkov light generated as the EAS
hits the detector. Milagro is one such detector, and has observed
high energy (~1TeV) gammas and protons from high energy cosmic
phenomena such as active galactic nuclei and supernova. A new detector
called HAWC (High Altitude Water Cherenkov), similar to Milagro
but with new electronics and high-altitude location (4000m), data
was taken at University of New Mexico to perfect the measurement
method and to characterize how other factors, such as weather,
tank configuration, and power sources affect count rates. Once
these variables were well understood, the detector was used to
measure particle flux at four different altitudes: 1540m, 2650m,
3231m, and 4308m. The rates of the low energy electromagnetic particles
were found to increase with altitude, and had values of 4.38 kHz,
4.82 kHz, 5.50 kHz, and 6.92 kHz, respectively. The 2650m data
was taken at the Milagro site as a reference point. Based on the
current data acquisition and analysis algorithm used for Milagro,
singles rates at the HAWC site should be less than a factor of
two greater then they are at Milagro. The rates measured at >4000m
were 1.44 times greater than the rates at Milagro, leading to the
conclusion that singles rates at a HAWC site >4000m will have
a negligible effect on triggering and pulse height measurement.
Conceptual Overview of the NPDGamma Experiment. JOSEPH JANOSIK (University
of Dayton, Dayton, OH, 45469) W. SCOTT WILBURN (Los Alamos National Laboratory, Los Alamos, NM, 87545)
The magnitude
of the weak force is not yet well defined. The NPDGamma experiment
at the Los Alamos Neutron Science Center will soon be taking data
that will place bounds on the hadronic weak coupling constant Hπ1.
This experiment uses polarized cold neutrons which capture on a
liquid hydrogen (proton) target, and emit gamma rays that have
a directional dependence on the spin of the incident neutrons only
according to the weak force. Thus, a measured asymmetry in gamma
ray detection can be used to extrapolate the weak coupling. The
asymmetry is expected to be very small, around 5 x 10-8,
so careful experimental design and construction have been executed
to ensure accuracy of this measurement. This document provides
a conceptual overview of the workings of this experiment.
Controlled Assembly of Protein-mediated Lipid Multi-bilayers. CONSTANCE ROCO (University
of Virginia, Charlottesville, VA, 22904) GABRIEL MONTAÑO (Los Alamos National Laboratory, Los Alamos, NM, 87545)
Protein-mediated
multilamellar lipid assemblies were created using biotin-streptavadin
conjugation. We are interested in using these assemblies as a platform
for investigating membranes and membrane-protein properties, as
well as towards understanding the relationship between structure
and function in biological multilamellar assemblies, such as the
neuron insulating myelin sheath. Successive lipid bilayers, containing
a fraction of biotinylated lipids, are held together using an intermediate
layer of streptavadin. Control over lipid bilayer assembly was
determined using atomic force microscopy and spectroscopic ellipsometry.
Lateral fluidity of individual layers was characterized by fluorescence
recovery after photobleaching (FRAP). Three successive bilayers,
with each successive bilayer exhibiting fluidity, have been created.
We are currently determining effects of protein concentration and
numbers of bilayers on fluidity by comparing rates of diffusion
under the various conditions. There are many other properties,
such as the substrate and lipid composition, that can affect membrane
interactions that can be altered and studied in future work. The
investigation of these biomimetic assemblies illustrates how guided
molecular self-assembling at the nanometer length scale can improve
our understanding of complex biological systems.
Hydrocode Simulations of Mach Stem Formation. STEPHEN DAUGHERTY (Vanderbilt University, Nashville, TN, 37235) DENNIS PAISLEY (Los Alamos National Laboratory, Los
Alamos, NM, 87545)
The study of
shock waves often makes use of metallic disks propelled at high
velocities to act as impactors. There are a number of ways to supply
flyers with energy, but it takes some scheming to achieve extreme
accelerations; a laser can focus a large amount of energy into
a small area, but at some point thermal effects will take over,
scattering much of the pulse energy and heating the sample. One
solution is to strike a cone with a high-energy pulse and allow
the resulting shock to converge toward the center. The shock reflected
from the center will move at supersonic speed behind the incident
shock, causing a flat energy disk—a Mach wave—to propagate through
the center of the cone. The Mach wave will carry a high energy
density to the base of the cone, where it can be transferred to
a flyer.
Jovian Planet Formation in 50 AU Binary Star Systems. CHRISTIAN LYTLE (University
of St. Thomas, St.
Paul, MN, 55105) ANDY NELSON (Los Alamos National Laboratory, Los
Alamos, NM, 87545)
The detection
of Jovian planets in large-separation binaries (>100 AU) has
motivated investigation into the probability of planet formation
in approximately 50 AU and smaller systems. We have run smoothed-particle
hydrodynamics (SPH) simulations of binary systems with circumstellar
disks and compared our results with others in the literature. Cooling
based both on a fraction of the orbital period and a fully radiative
model are implemented, but neither produce gravitational instabilities
of the magnitude required for long term fragmentation of the disks,
due primarily to the strong heating which occurs when the disks
are near periapse. These results are in conflict with simulations
from the literature that have produced fragmentation in disks with
morphologies similar to ours. We propose that the inconsistencies
are attributable to numerical deficiencies (low resolution and
fixed gravitational softening) and unrealistic initial conditions
present in the previous work.
Nanosecond-length Electron Pulses for a Time-of-Flight Mass Spectrometer. LIANNE MARTINEZ (University of Nevada Las Vegas, Las
Vegas, NV, 89123) HERBERT FUNSTEN AND PAUL JANZEN (Los Alamos National
Laboratory, Los Alamos, NM, 87545)
The Spatially
Isochronous Time-of-Flight (SITOF) mass spectrometer is a rapid
mass analysis of gaseous samples at a high mass resolution in a
small volume. The mass spectrometer incorporates a pulsed
electron ionization source within the drift region itself, eliminating
a separate ion source and its associated mass, power, and volume
resources. Gas in the drift region is ionized at the same time
by the pulsed electron source, and the ions are accelerated by
a linear electric field in the drift region so that their time-of-flight
in the drift region is independent of the location at which they
were ionized. The current proof-of-concept pulsed electron source
uses a channel electron multiplier stimulated by a weak radioactive
source to produce electron pulses approximately 10 ns long. These
pulses have been characterized, and development has started on
a pulsed electron source which uses a microchannel plate stack
to multiply photoelectrons produced from a fast ultraviolet LED.
This method produces electron pulses of a shorter duration, over
a larger area, at a controllable frequency. We discuss the time
dispersion of the pulsed electron source, its dependence on detector
bias and gain, and its impact on the mass resolution of the SITOFS
mass spectrometer.
Optimization of Shield Mass for a Low Power, Fast-Spectrum Liquid-Metal Cooled
Surface Reactor System. ROBERT FORESMAN (Pomona College, Claremont, CA, 91711)
DAVID I. POSTON (Los Alamos National Laboratory, Los Alamos, NM, 87545)
Extending our
presence farther into space furnishes opportunities for research
science, potential human colonization beyond Earth, and a more
mature understanding of the cosmos. One of the foremost challenges
in this effort is the identification of a low-cost power source
that will accommodate scientific instrumentation and mission necessities
for long periods of time. Low power nuclear reactors that utilize
well-tested materials and concepts such as stainless steel and
water shields can operate in the 25 kW electrical range. By short-circuiting
exotic designs, these reactors reduce the cost and time of development
in the face of a strict US budget. Gamma radiation dose to the
Stirling alternator power conversion system and total astronaut
dose can be kept to their nominal minimums of 20 MRad and 5 Rem/yr
by burying the reactor in lunar surface material (regolith) on
Moon missions.1 An alternative option is to install a permanent water shield
on the reactor. Minimization of additional shield mass for such
a system is an interesting engineering problem that is ideally
suited to a radiation transport software program called MCNPX (Monte
Carlo Neutral Particle). MCNPX output files contain criticality
statistics to ensure a stable reaction and allow direct determination
of dosages. Shield thickness, placement of interstitial, high-Z
shield elements, and boron concentration in shield water will be
treated as variables for system optimization. Initial simulations
show that roughly 93% of the gamma dose to astronauts at 800 meters
from the reactor core is due to radiative capture in the water
shield. A borated water shield that meets astronaut dosage requirements
and has a total mass of roughly 5,000 kg can be constructed utilizing
interstitial stainless-steel layers of varied thickness. This total
shield mass of 5000 kg must be compared to the total mass of a
buried system configuration including burying equipment. Further
investigations include the addition of different shielding materials
such as depleted uranium throughout the shield as well as moving
the reactor core off-center within the water shield. 1Marcille,
T. F., Dixon, D. D., Fischer, G. A., Doherty, S. P., Poston, D.
I., and Kapernick, R. J. Design Of a Low Power, Fast-Spectrum,
Liquid-Metal Cooled Surface Reactor System. Nuclear Systems Design
Group, Los Alamos National Laboratory, Los Alamos, NM 87544., pp
1-3.
Protection of Aluminum from Saltwater Corrosion by
Superhydrophobic Films. PHILIP
BARKHUDAROV (Utrecht University, Utrecht, ND, 0) JAROSLAW MAJEWSKI (Los Alamos National Laboratory, Los
Alamos, NM, 87545)
The damaging
effects of corrosion cost billions of dollars each year in metal
replacements and repairs. Unfortunately, corrosion cannot be completely
stopped; the natural state of most metals on earth is in oxide
form. Fortunately, it is possible to slow the oxidation process
or to redirect it, and with ever more advanced technology, especially
on the nano-scale, corrosion prevention is becoming more and more
effective. This research focused on the corrosion of aluminum in
salt-water environments. In dry air, aluminum develops a thin surface
oxide layer that prevents further corrosion. However, in the presence
of water and salt, this layer is broken and rapid corrosion ensues.
In this study, superhydrophobic films were layered onto the metal,
repelling water and slowing corrosion. These superhydrophobic films
consisted of a highly nano-porous silica framework together with
hydrophobic organic ligands. To study the effectiveness of such
protective layers, the neutron reflectometry method was used. By
taking neutron reflection measurements over time on samples of
layered aluminum/superhydrophobic film/salt-water, it was possible
to observe and quantify the rate of oxide growth in the aluminum.
From the relatively short period of measurement, it was possible
to predict corrosive behavior on a longer time scale and to show
the effectiveness and feasibility of using superhydrophobic films
to protect aluminum in marine environments, i.e. ships, off-shore
platforms, aircraft, and coastal regions.
Protein Purification on Tuberculosis Protein. ASHLEY JONES (Fisk University, Nashville, TN, 37208) DR. CHANG YUB KIM (Los Alamos National Laboratory, Los Alamos, NM, 87545)
Tuberculosis
(TB), caused by Mycobacterium tuberculosis (M. tb), is an infectious
disease known to affect the lungs in most cases. In 2004, there
were about 14.6 million people with latent TB including nine million
new cases. Over 2 million people die every year from this disease.
Although different drugs have been developed to fight this disease,
these drugs are no match for the spontaneous mutations of this
deadly disease with new M.tb strains resisting multi-drugs. Thus
scientists continue to look for new methods to combat this disease.
After the completion of sequencing TB genome, TB Structural Genomics
Consortium was established to determine the structure for over
400 proteins. Since 2000, the Los Alamos National Laboratory (LANL)
has partaken in this Structural Genomics project by cloning and
purifying target proteins. The purified proteins are to be used
in determining the three dimensional structure of the protein and
ultimately its function. Eventually, this will allow scientists
to produce a pharmaceutical drug that will inhibit the protein,
which will then stop TB. In this paper, we will discuss the developed
protocol of protein purification and the role that I played in
the purification process this summer.
Star Formation and Feedback in Adaptive Mesh Refinement
Cosmological Simulations. SAM
SKILLMAN (Harvey Mudd College, Claremont, CA, 91711) BRIAN O'SHEA (Los Alamos National Laboratory, Los
Alamos, NM, 87545)
Correctly simulating
star formation within large-scale cosmological simulations is currently
a problem of great interest. This is in part due to the recent
explosion of observational data from projects such as the Sloan
Digital Sky Survey, DEEP, and 2dF. Using ENZO, an adaptive mesh
refinement(AMR) with N-body plus hydrodynamics cosmological code,
I explore three star formation algorithms which lead to a range
of star formation histories. Stellar feedback models are coupled
to each of the star formation algorithms, and provide thermal,
kinetic, and metal feedback in our simulations. Each star formation
algorithm uses several parameters which I vary in order to gain
an understanding of their effect on the star formation history
of the universe.
