Student Abstracts at LANL:

A New Routing Protocol for Connectivity in Ad Hoc Networks. TYLER KARRELS (University Of Wisconsin - Madison, Madison, WI, 53703) SAMI AYYORGUN (Los Alamos National Laboratory, Los Alamos, NM, 87545)

TCP/IP routing is the standard for static wired networks, but TCP/IP cannot quickly adjust to changes in network topology that can occur in wireless ad hoc networks. A wireless ad hoc network's topology is dynamic because hosts eventually lose power, hosts' transmission ranges may vary over time, hosts may become damaged, or hosts may enter or exit the network's transmission range. These problems require new routing paths to be established to maintain network connectivity. The purpose of our research at Los Alamos National Lab (LANL) is to improve, or at least maintain, connectivity between hosts even when the network topology is drastically altered. We propose a new routing protocol called Neighbor Monitoring (NM) that creates multiple paths to the network sink and monitors these paths to decide which is optimal. Network simulations have been conducted in Matlab using a simulator developed for this research. For a comparison to existing routing algorithms, Dynamic Source (DSR) and Load Balance (LB) routing algorithms have been implemented in addition to NM routing. Simulations are being run with networks of varying size and topology. The three topologies used are grid, random, and degree based. Preliminary results for small networks have shown that DSR and LB algorithms perform better than NM in a grid network topology and no node failures. It is expected that NM routing will be more resilient by quickly repairing routes. It is also expected that NM routing will establish quicker routes even when a network is heavily loaded.

A Radiochemical Separation of Selenium and Arsenic Using a BioRad Ag1-X8 Resin Column. PAWAN RASTOGI (Columbia University, New York, NY, 10027) MICHAEL FASSBENDER (Los Alamos National Laboratory, Los Alamos, NM, 87545)

Although classified as a group 1 carcinogen by the International Agency for Research on Cancer, arsenic and its compounds have proven to have many potential uses in nuclear medicine. Isotopes of arsenic, such as ⁷⁴As and ⁷²As, have been used in Positron Emission Tomography (PET). ⁷²As is a positron emitting isotope with a 26 hour half life (T_½) and mean positron energy (E_B+mean) of 1.2 MeV. These characteristics lead ⁷²As to be a promising candidate for being incorporated into radiopharmaceuticals. Such ⁷²As-labeled radiopharmaceuticals can be used in quantitative imaging of different biochemical and physiological processes. Here the delivery route for radioarsenic is considered via the production of a radionuclide generator parent like ⁷²Se, which, in turn, will decay into ⁷²As. A potential portable radioarsenic generator will be of value due to transportability and efficacy in delivering the radioisotopes to hospital and university settings. The main objective in this study was to develop an As/Se separation system that could be used in the future for a radionuclide medical generator. A strongly basic anion exchange resin (BioRad Ag1-X8) column was used to separate arsenic from selenium with different concentrations of ammonium chloride (NH4Cl). Radioarsenic was seen to elute with 0.01M NH₄Cl and 0.2M NH₄Cl. Generally all radioselenium retained on the column, but a small amount (~0.1%) was seen to elute with a 0.5M NH₄Cl eluent. The different retentions of radioarsenic and -selenium on the resin column support that more than one species of As and Se are present within the matrix. Due to time constraints speciation of the effluent was unable to be conducted. This preliminary separation of radiotracer quantities of arsenic and selenium shows much potential in developing a system fit for radionuclide generators. Future hopes include optimization of separation, characterizing the species involved in the matrix system, and development of a biologically deliverable form of the radioarsenic. The purpose of this paper is to report a method to separate arsenic from selenium using a BioRad Ag1-X8 anion exchange resin column with an ammonium chloride elution system.

Effective Queue Distributions in Video Streaming: A User Perspective. R BENJAMIN CLAY (Virginia Tech, Blacksburg, VA, 24060) SAMI AYYORGUN (Los Alamos National Laboratory, Los Alamos, NM, 87545)

Queuing theory and buffer control are areas of great interest as networks become large and unmanageable. Specifically, guaranteeing a quality of service (QoS) in a large, uncontrolled network such as the internet is important from both a business perspective (selling a service at a specified QoS) and a users perspective. In order to ensure that data reaches the intended target at the intended rate, stochastic rate control algorithms can be used to guarantee a service within a given probability. To this end, previous work has determined and elaborated upon mathematical methods to achieve optimum buffer control given a generic packet-based data source. Our work extends these algorithms to streaming video, using subjective analysis to determine the appropriate equations and values to make the rate control transparent to the end user. To do so, a server-client implementation has been built on top of the popular opensource video player VLC. The rate control algorithms specified in previous work are built as the core of the server application, modifying VLC’s UDP streaming server component. The client is another copy of VLC, operating as a UDP streaming client. Preliminary results indicate correlation between decay rate and video quality for those distributions that employ a decay rate.

Frequency Quadrupled DUV Laser for Ytterbium 2+ Spectroscopy. JOHN OGREN (The University of New Mexico, Albuquerque, NM, 87131) JUSTIN TORGERSON (Los Alamos National Laboratory, Los Alamos, NM, 87545)

In the case presented, Ytterbium ²⁺ (Yb²⁺) was being sought in a linear RF trap. In order to detect and then laser cool the Ytterbium²⁺, the ¹S₀ to ³P₁ transition at 252 nm was chosen due to the fast transition period of 231 ns. In order to excite this transition a laser system at 252 nm was needed that was widely tunable and had a narrow linewidth. There were no commercially produced laser systems that fulfill these requirements. The proposed solution to this problem was to frequency quadruple a commercially available Titanium-Sapphire (Ti-Sapph) laser from 1008 nm to 252 nm. The titanium doped sapphire crystal was within a monolithic block resonator (MBR) and, when lasing, was tunable over a wide range of wavelengths (approximately 700 nm to 1100 nm) with a linewidth of approximately 100 kHz. This provided the necessary flexibility needed for the spectroscopic and cooling applications. A Potassium Niobate (KNbO₃) crystal was mounted within the MBR cavity and frequency doubled the initial Ti-Sapph beam from 1008 nm to 504 nm. The resulting beam was then doubled again using an external doubling cavity with a ß-Barium Borate crystal (BBO). Currently, 12 W from a Diode Pumped Solid-State Continuous Wave (DPSS CW) laser, operating at 532 nm, pumps the MBR which produces roughly 50 mW at 503 nm through the KNbO₃. As of recently, 2 mW of power has been output from the BBO. In addition, the linewidth is no more than 400 kHz and is tunable over several GHz. These excellent results encourage the use of frequency quadrupling techniques to retain the original characteristics of commercial lasers while fitting the system to the specific needs and goals of a project.

Modeling of an Aerosol Collection Inlet for Interior Monitoring. ROBERT IGEL (Bradley University, Peoria, IL, 61606) DAVID DECROIX (Los Alamos National Laboratory, Los Alamos, NM, 87545)

The dispersion of biological agents into populated environments is a serious terrorist threat faced by the United States. Possible targets of biological terrorism include densely populated areas such as stadiums and public transportation systems. Los Alamos National Laboratory wants to be able to collect air samples in these areas using an aerosol inlet for a collection device that has been designed to be installed in the HVAC system of densely-populated buildings. The inlet was designed to collect particles less than 10µm. Preliminary testing has been performed on this design; however, a more complete understanding of the inlet was desired. The purpose of this research was to model the same inlet using the Fluent computational fluid dynamics solver to provide more conclusive collection efficiency results and determine the flow characteristics caused by the inlet. The 3-D model of the design, its mesh, and its boundary conditions were constructed in Gambit. This file was then exported into the Fluent solver, where flow conditions - turbulence, flow rate, and particulate size - were specified. Several wind tunnel tests were run varying the free stream velocity between 2- and 8km/hr and particulate sizes of 8-, 12-, and 20µm. The results of these experiments show that the inlet will collect the vast majority of the 8-µm particles, only a small percentage of the 12-µm particles, and none of the 20-µm particles. However to determine the streamlines and other flow properties of the inlet geometry and its overall efficiency, computational simulations have been run. The results from this research will better enable the detection of biological agents harmful to building occupants.

Multiplexed Assemblies for SERS-Detection Applications. CHRISTINA BRADY (University of California, San Diego, San Diego, CA, 92092) STEPHEN DOORN (Los Alamos National Laboratory, Los Alamos, NM, 87545)

Raman techniques offer advantages over the well-established fluorescence in detection applications and microscopic analysis. Unlike fluorescence, Raman spectroscopy generates narrow peak widths allowing for a distinct fingerprint spectrum and easy identification of a material; however, low signal strength from Raman spectroscopy has limited its practical applications. Raman applications have increased with the use of Surface Enhanced Raman Scattering (SERS). To overcome weak signal strength, metal nanoparticles, such as gold or silver, are used as substrates for the attachment of the signal dye. Various attempts have been made to optimize the Raman signal by allowing the combination of different signal dyes for a single SERS-active nanoparticle. To achieve this, current research at Los Alamos National Laboratory involves synthesis of multiplexed nanoparticle assemblies to give a combination of signals. Silver (Ag) nanoparticles approximately 60nm in diameter were tagged with a particular Raman dye, aggregated, and silica coated. The tagged Ag particles were attached to silicon microspheres via biotin-avidin interactions in different dye ratios. Raman spectroscopy and Raman microscopy were used to measure and characterize the signal strength of the particles. Results showed that optimization of Raman signals occurred with the aggregation of Ag nanoparticles due to increased surface plasma resonance between the particles. Attachment chemistry of SERS-active nanoparticles to the silicon bead and dye combination spectra are currently being analyzed. Multiplexed nanoparticles can be used in further experiments requiring SERS-detection of different substrates simultaneously. Future synthesis of multiplex particles with different combination of dyes will allow for a larger array of dye spectra than currently available.

Performance Comparison between 10GigE and InfiniBand in high performance computing. COLBY BOYER (University of California, Berkeley, Berkeley, CA, 94720) CAROLYN M. CONNOR (Los Alamos National Laboratory, Los Alamos, NM, 87545)

The processing power of a large computing cluster relies heavily on its ability to transmit data quickly among its numerous nodes. This requirement demands that the network interconnects have both low latency and high bandwidth. Currently, the most popular form of interconnect in high performance applications is InfiniBand (IB), because it offers both low latency and high bandwidth. The recently released 10 Gigabit Ethernet (10GigE) standard offers similar bandwidth and slightly worse latency performance as compared to the IB 4x. Despite its drawbacks, 10GigE can be more easily integrated into the common Ethernet network than IB because 10GigE uses the Ethernet protocol and IB does not. To determine 10GigE Message Passing Interface (MPI) performance, MVAPICH2 MPI benchmarks will be run over native InfiniBand and 10GigE with Remote Direct Memory Access (RDMA), and in addition MPICH2 MPI benchmarks will compare IP over IB(IPoIB) and 10GigE without RDMA. These benchmarks measure the MPI bandwidth and latency performance. The bandwidth comparison between 10 GigE with RDMA and InfiniBand are nearly equal but 10 GigE provides slightly higher bandwidth. With small message sizes the latency comparison shows IB with two to three times lower latency as compared to 10 GigE with RDMA. IPoIB and 10 GigE without RDMA both performed worse than IB and 10 GigE with RDMA, because the RDMA used by IB and 10 GigE allows for Operating System bypass(OS bypass). The poor test results of IPoIB and 10 GigE without RDMA show that OS bypass is key for high network performance. Even though the performance between IB and 10 GigE with RDMA are similar, IB still remains significantly cheaper than 10 GigE because 10 GigE is a newer technology. Future testing with production level MPI software should be conducted to determine what effect the latency difference between the two has on performance.

Practical DNA-based Clinical Diagnostics. DAVID GEB (University of California, Los Angeles, Los Angeles, CA, 90095) TORSTEN STAAB (Los Alamos National Laboratory, Los Alamos, NM, 87545)

The development of a disposable test cartridge for DNA-based clinical diagnostics will afford a better alternative to current protein-based tests. DNA-based clinical diagnostics is significantly more accurate than the protein-based alternative. Moreover, a cheap, effective, disposable test cartridge will allow this technology to be accessible to more patients. The development of this test cartridge involves designing, prototyping, assembling, and testing its mechanical components. After the completion of the project, a user-friendly, affordable, and accurate device will be the result. Its technology will provide a solution for clinical diagnostics in physician offices worldwide.

Redox Reactions wiith Single-Walled Carbon Nanotubes. SOFIANE BOUKHALFA (University of Illinois at Urbana-Champaign, Urbana, IL, 61801) STEPHEN DOORN (Los Alamos National Laboratory, Los Alamos, NM, 87545)

Single Walled Carbon Nanotubes (SWNT) have been under close scrutiny by the scientific community since their discovery in 1992 due to their surprising material properties. SWNT synthesis can be achieved in numerous ways. However, these methods result in a wide spectrum of chiralities of nanotubes. In order to more efficiently use these novel materials, individual chiralities must be isolated. To achieve this, a reduction-oxidation chemistry approach is used. Redox reagents of different electro-chemical potentials were added to solutions of SWNT in surfactant. Spectroscopy (absorbance and fluorescence) measurements were taken in order to monitor the effects of electron transfer between the SWNTs and the salts. Once chiral-specific doping can be achieved, isolation of these individual chiralities of SWNTs is planned through the use of ultracentrifugation. 20µL of each redox reagent was added to 3mL SWNT in surfactant solution while spectroscopy measurements were taken every 7 seconds in order to map out chiralities. Using a Fermi level map of the chiralities as a model, it was determined that the electro-chemical potential of the reagents directly affected the chiralities which were quenched during the experiments. Interaction between the salt and the surfactants is characterized by aggregation of the SWNTs; in the current redox reactions such aggregation, which broadens the spectroscopic signals, is not observed. Thus, a direct correlation was determined between the electro-chemical potential of the redox reagent and its effects on the nanotube solutions. This work establishes a future guideline for new work in the isolation of individual chiralities of nanotubes.

Shielded Active Integrators for use in Plasma Magnetic Field Diagnostics. IAN FAUST (University of Michigan, Ann Arbor, Mi, 48109) TOM INTRATOR (Los Alamos National Laboratory, Los Alamos, NM, 87545)

The Field Reversed Experiment (FRX-L) at Los Alamos National Laboratory confines deuterium plasma in a compact toroidal shape known as a Field Reversed Configuration (FRC). The characterization of the plasma necessitates the analysis of its magnetic fields. Through the use of Faraday’s induction law, an electrical signal from a “b-dot” probe must be integrated accurately to understand the strength and nature of the induced magnetic field. Integration of the signal is done precisely using an analog active integrator. It allows for substantial gains, automatic zeroing of the baseline integrated signal and no signal droop, reducing the error. Data accuracy is preserved through diligent shielding from electromagnetic interference. This was done by mounting the cards within a standard rack chassis isolated in a faraday cage-like arrangement. The design has been optimized to reduce cross-interference, ease repairs and reduce temperatures. The overall error and noise fluctuations are expected to be reduced significantly by many orders of magnitude. Magnetic signal analyses, which comprise the primary diagnostic for the FRC, require one to difference two integrated dB/dt signals. This differential integrator provides a simple way to do this electronically without manually zeroing out integrating signals. The increased precision will allow for better characterization of the plasma in the upcoming tests on FRX-L. Depending on the time scales and characteristics of future plasmas, adjustments to longer timescales and greater shielding will necessitate modification of the active integrator.

Variance Reduction for Radiation Transport using Delta-f Methods. IAN PERCEL (University of Illinois at Urbana-Champaign, Urbana, IL, 61801) RICK NEBEL (Los Alamos National Laboratory, Los Alamos, NM, 87545)

Radiation hydrodynamics is employed by physicists to describe the behavior of fluids that are strongly coupled to a radiation field. This is particularly important in analyzing astrophysical phenomena. Direct Simulation Monte Carlo is one of the few numerical tools available for solving realistic problems in radiation hydrodynamics. Since M. Kotschenreuther's work in 1988, the delta-f method has dramatically reduced the variance observed in Monte Carlo solutions to problems in plasma physics. Recently, researchers at Lawrence Livermore National Laboratory (LLNL) have considered using a similar technique in radiation transport. The new algorithm being studied at Los Alamos National Laboratory (LANL) includes the LLNL algorithm as a special case. The LANL equilibrium term results from using the standard asymptotic expansion to include diffusion as well as the Local Thermal Equilibrium component that the LLNL algorithm is restricted to. The weighting function is evolved using a difference equation for the total time derivative of the distribution. The connection to the weighting function is established by using a Klimontovich representation of the system. In this research, the proposed change has been formally proven to provide a valid extension of the delta-f method. The derivation also implies the existence of an alternate evaluation method that may provide a check on the diffusion approximation. If efficiency gains observed in plasma physics simulations hold, the new algorithm should show a dramatic improvement over the LLNL algorithm. Specifically, the new algorithm may offer as large a gain in efficiency over the LLNL algorithm as the LLNL algorithm demonstrates when compared with analog methods. A comparison of the two algorithms has not been completed and continuing work should provide a basis for further improvements. This algorithm may offer significantly more accurate radiation transport calculations than have been possible to date. Initial numerical results will be presented.