Browsing by Author "Wesley E. Snyder, Committee Member"

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The Analysis and Identification of Protein-coding Sequences for Yeast Using a Free Energy Model
(2007-08-15) Xing, Chuanhua; Wesley E. Snyder, Committee Member; Steffen Heber, Committee Member; Anne-Marie Stomp, Committee Member; Winser E. Alexander, Committee Co-Chair; Donald L. Bitzer, Committee Co-Chair; Mladen A. Vouk, Committee Member
Benchmarking Thermal Neutron Scattering in Graphite
(2007-12-21) Zhou, Tong; Wesley E. Snyder, Committee Member; Mohamed A. Bourham, Committee Member; Bernard W. Wehring, Committee Member; Ayman I. Hawari, Committee Chair
The Very High Temperature Reactor (VHTR), one of the Generation IV reactor concepts, is a helium-cooled, graphite-moderated nuclear reactor with a core temperature reaching 1000°C. It can provide high quality process heat for hydrogen production beside power generation and will become deployable around 2030. At such temperature, graphite is an appropriate neutron moderator material due to its high sublimation temperature and high temperature strength. Furthermore, graphite has a large heat capacity and stable structure due to its large thermal inertia. However, the current thermal neutron cross-section libraries of graphite are based on models and data developed in the 1950s and 1960s. Significant discrepancies between measurements and the computational predictions of these libraries were observed. As a result, a study was performed in this dissertation to benchmark modern and traditional thermal neutron scattering libraries of graphite. In this work, a Slowing-Down-Time experiment was designed and performed at the Oak Ridge National Laboratory (ORNL) by using the Oak Ridge Electron Linear Accelerator (ORELA) as a neutron source to study the neutron thermalization in graphite at room and higher temperatures. The MCNP5 code was utilized to simulate the detector responses and help optimize the experimental design including the size of the graphite assembly, furnace, shielding system and detector position. To facilitate such calculation, MCNP5 version 1.30 was modified to enable perturbation calculation using point detector type tallies. By using the modified MCNP5 code, the sensitivity of the experimental models to the graphite total thermal neutron cross-sections was studied to optimize the design of the experiment. Measurements of slowing-down-time spectrum in graphite were performed at room temperature for a 70x70x70 cm graphite pile by using a Li-6 scintillator and a U-235 fission counter at different locations. The measurements were directly compared to the Monte Carlo simulations that use different graphite thermal neutron scattering cross-section libraries. Simulations based on the ENDF/B-VI graphite library were found to have a 30%-40% disagreement with the measurements. In addition to the graphite SDT experiment, which provided the data in the energy region above the graphite Bragg-cutoff energy, transmission experiments were performed for different types of graphite samples using the NIST 8.9 Å beam (located at NG-6) to investigating the energy region below the Bragg-cutoff energy. Measurements confirmed that reactor grade graphite, which is a two phase material (crystalline graphite and amorphous carbon), has different thermal neutron scattering cross section from pyrolytic graphite (crystalline graphite). The experiments presented in this work compliment each other and provide an experimental data set which can be used to benchmark graphite thermal neutron scattering cross section libraries that are generated using different methodologies. Further investigation is necessary.
Engineering Methodologies and Design Concepts for Systems Biology
(2008-06-26) Williams, Cranos Monroe; Winser E. Alexander, Committee Chair; William W. Edmonson, Committee Co-Chair; Wesley E. Snyder, Committee Member; Anne Stomp, Committee Member; Mladen A. Vouk, Committee Member
Prompt Gamma-ray Imaging for Small Animals
(2006-11-02) Xu, Libai; Avneet Sood, Committee Member; Dmitriy Y. Anistratov, Committee Member; Robin P. Gardner, Committee Chair; Wesley E. Snyder, Committee Member
A new imaging modality called prompt gamma-ray imaging (PGI) has been identified and investigated primarily by Monte Carlo simulation. Currently it is suggested for use on small animals. This new technique could greatly enhance and extend the present capabilities of PET and SPECT imaging from ingested radioisotopes to the imaging of selected non-radioactive elements, such as Gd, Cd, Hg, and B, and has the great potential to be used in Neutron Cancer Therapy to monitor neutron distribution and neutron-capture agent distribution. This approach consists of irradiating small animals in the thermal neutron beam of a nuclear reactor to produce prompt gamma rays from the elements in the sample by the radiative capture (n, γ) reaction. These prompt gamma rays are emitted in energies that are characteristic of each element and they are also produced in characteristic coincident chains. After measuring these prompt gamma rays by surrounding spectrometry array, the distribution of each element of interest in the sample is reconstructed from the mapping of each detected signature gamma ray by either electronic collimations or mechanical collimations. In addition, the transmitted neutrons from the beam can be simultaneously used for very sensitive anatomical imaging, which provides the registration for the elemental distributions obtained from PGI. The primary approach is to use Monte Carlo simulation methods either with the specific purpose code CEARCPG, developed at NC State University or with the general purpose codes GEANT4 or MCNP5, to predict results and investigate the feasibility of this new imaging idea. Benchmark experiments have been conducted to test the capability of the code to simulate prompt gamma rays, which are produced by following the nuclear structures of each irradiated isotope, and coincidence counting techniques, which are considered the most important improvement in neutron-related gamma-ray detection applications to reduce gamma background and improve system signal-to-noise ratios. With coincidence prompt gamma rays available, two major imaging techniques, electronic collimations and mechanic collimations, are implemented in the simulation to illustrate the feasibility of imaging elemental distribution by this new technique. The expectation maximization algorithm is employed in electronic collimation to reconstruct images. The common SPECT imaging algorithms are used in mechanical collimation to get an image. Several critical topics concerning practical applications have already been discussed, such as the radiation dose to the mouse and the detection efficiency of high-energy gamma rays.
Textile-embedded Sensors for Wearable Physiological Monitoring Systems
(2007-05-19) Kang, Tae-Ho; H. Troy Nagle, Committee Chair; Wesley E. Snyder, Committee Member; Bradley Vaughn, Committee Member; Edward Grant, Committee Member; Behnam Pourdeyhimi, Committee Member
For long-term physiological monitoring inside or outside a hospital setting, a reliable, wearable monitoring system would be a convenient platform if biomedical sensors are securely placed in appropriate positions. An article of clothing is an attractive platform to implement such a wearable system. It is highly desirable that the sensors be designed and integrated into the garment in an unobtrusive way. The purpose of the dissertation is to develop textile-embedded biomedical sensors that can be integrated into textile substrates in a seamless manner for long-term ECG and respiration monitoring while normal daily activities including walking, jogging, sleeping, sitting, and other exercise are transpiring. These sensors should provide both a comfortable textile interface and robustness against noise and motion artifacts. For ECG monitoring, we developed textile-embedded active electrodes that transform high input impedance signals to low impedance versions by employing a voltage follower circuit. The fabric active electrodes include a transducer layer on the top of the nonwoven substrates and a circuit layer on the bottom. The transducer area, signal path and power lines are filled with Ag⁄AgCl ink by screen printing or hand painting. The electrical components and external wires were attached using adhesive conductive inks and protected by another textile covering layer. For respiration monitoring, we devised a fabric sensor structure based on double nonwoven substrates. Stretchable and non-stretchable segments of nonwoven fabrics are laterally attached by, for example, ultra sonic bonding. The stretchable fabrics are employed in belts around the chest and abdomen and respond to breathing effort by changing the sensor's length in the direction of the strain applied. Rectangular plates for a capacitive sensor or an open-rectangular spiral for an inductive sensor is deposited on the non-stretchable fabric portions of the sensors by printing or painting silver ink. Their relative positions change when the stretchable portion activates. Each plate is initially placed so that the conducting areas overlap minimally. As the stretchable portions of the device are exercised, the two plates slide in opposite directions, changing the effective area and hence the capacitance or inductance values. These capacitance or inductance variations are transformed into voltage outputs by electronic circuits individually designed for each sensor. For single and differential modes of operation in the capacitive sensor, various electrode patterns are suggested. For the inductive sensor, various configurations of spirals are presented to form three different types of planar inductive displacement sensors: a single inductor sensor, a transformer-type differential sensor, and an autotransformer-type differential sensor. In addition to the design based on double substrates, we demonstrate a respiratory inductive sensor based on a single substrate. To form an inductive sensing area, fine magnet wires are stitched on a stretchable nonwoven substrate. The textile substrates supporting the conducting materials are then laminated to stabilize the geometric structure relationships and mechanically protect the sensor. Finally, we transform these textile-embedded sensors into a wearable human physiology monitoring system. The various elements of the system are described. Finally, we discuss the possibility of using the system for sleep apnea detection and sleep staging.