2008 Bowman Scholars
Division of Engineering and Weapons
- 1/C John T. Hayashi
- Major: Mechanical Engineering
- Title: MCNP5 Modeling of the DT-702 Thermoluminescent Dosimeter
- Advisor: Professor Martin E. Nelson, Mechanical Engineering Department Abstract
MCNP5 Modeling of the DT-702 Thermoluminescent Dosimeter
The objective of this research project is to use Monte Carlo modeling techniques to virtually model current Navy standard DT-702 thermoluminescent dosimeter (TLD). The DT-702 TLD contains four manganese-copper-phosphorus (MCP) doped LiF chips that are held on an aluminum card contained in a plastic holder. The first task will be to create a virtual model of the DT-702 response using MCNP5 (Monte Carlo N-Particle Transport Code, version 5) computer software. The second task will be to integrate the DT-702 model into a NIST irradiation room MCNP model, which was created by last year’s Bowman scholar, MIDN Travis Albright. The third task will be to run the model with the DT-702 TLD replaced with an ionization chamber. This last model will then serve to develop a calibration factor through comparisons with experimental data collected at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland.
The visual editing program, Moritz, will be used to draw and view the parts of the TLD. Using Moritz, a model consisting of a Cs-137 gamma source, the NIST irradiation room and the TLD attached to a methyl methacrylate material phantom, will be drawn. The methyl methacrylate is a material whose properties are equivalent to human tissue, which allows for comparisons between the model and real life. The MCNP5 program simulates particle interactions or energy deposition with the four LiF chips within the DT-702 by using Monte Carlo techniques. The number of particles is then converted to an equivalent dosage using conversions created from the NIST data. The MCNP program provides statistical significance, by running a large number of case histories, which if necessary, can involve billions of particles.
The primary objective for the project is to understand the relationship between gamma and beta radiation and the corresponding thermoluminescence of the doped LiF chips. By having a functioning virtual model, tests can be performed on different types of radiation fields in order to predict the response of the TLD to actual radiation fields.
- 1/C Collin R. Hedges
- Major: Mechanical Engineering
- Title: Investigation of HYSTOR 104 for Use in a Metal Hydride Powered Diver Heating / Cooling Unit
- Advisor: Professor Keith W. Lindler, Mechanical Engineering Department Abstract
Investigation of HYSTOR 104 for Use in a Metal Hydride Powered Diver Heating / Cooling Unit
The goals of this research project are to test the suitability of the metal hydride HYSTOR 104 for use in a diver heating/cooling unit and to compare the performance of HYSTOR 104 with previously tested metal hydrides. A metal hydride is a metal that can store hydrogen ions in its crystal structure through either ionic bonding or by absorbing the ions in interstitial spaces of the crystal structure. Since the hydrogen is stored within the crystal structure of the metal, a large amount of hydrogen can be stored in a small volume. Various metals can act as a metal hydride, each having unique thermodynamic properties. The properties of interest in this study are heat of absorption and equilibrium pressure. When two dissimilar metal hydrides are connected in a closed system, hydrogen will flow from the high pressure metal hydride to the low pressure metal hydride. This exchange of hydrogen causes an exothermic reaction at the low pressure metal hydride and an endothermic reaction at the high pressure metal hydride. These thermal reactions can provide either cooling or heating for divers. Since no hydrogen is lost to the environment, the process can be reversed by heating the low pressure metal hydride, and cooling the high pressure metal hydride. Because metal hydrides store large amounts of hydrogen and do not permanently consume hydrogen during the thermal reactions, metal hydrides provide a reusable, compact, and efficient cooling or heating source.
To test HYSTOR 104’s suitability as a low pressure metal hydride, HYSTOR 104 will be paired with various high pressure metal hydrides. For testing HYSTOR 104 will be surrounded by water and connected to a high pressure metal hydride. Once hydrogen is allowed to flow from the high pressure metal hydride to HYSTOR 104, the total heat released and the heating rate of HYSTOR 104 will be measured by observing the temperature increase in the water surrounding HYSTOR 104 and measuring the mass change in HYSTOR 104. By comparing these results to previous metal hydride tests, HYSTOR 104’s practicality as a heating source can be determined. In addition to measuring HYSTOR 104’s total released heat and heating rate, the reversibility of the metal hydride pair will be tested. This reversibility test will involve heating HYSTOR 104 and cooling the high pressure metal hydride to drive hydrogen from the HYSTOR 104 back to the high pressure metal hydride. Finding a candidate low pressure metal hydride for a diver heating/cooling unit will provide Navy divers with improved reusable thermal protection. This thermal protection will allow Navy divers to have greater comfort, longer on station time, and greater resistance to fatigue.
- 1/C Catherine M. Ortman
- Major: Ocean Engineering
- Title: The Effect of Diameter on Seabed Penetrometer Dynamic Performance
- Advisor: Commander Patrick J. Hudson, USN, Naval Architecture and Ocean Engineering Department Abstract
The Effect of Diameter on Seabed Penetrometer Dynamic Performance
This research project involves an investigation of seafloor embedment depth of objects larger than three inches in diameter. The goals of this project are (1) to better understand the soil dynamics involved in seafloor penetration; and (2) to improve upon the existing algorithms for prediction of penetration depth. Improvements of the existing algorithms will be made for the purpose of better predicting the depth of penetration into the seafloor of objects larger than three inches in diameter. The new algorithms may be used to predict the depth to which an object will penetrate or the force required for a specified depth penetration. These algorithms could apply to objects such as gravity anchors, gravity corers and penetrometers, and propellant-embedded anchor plates. Application of this research also applies not only to the Navy, but to oil extraction, pile driving, and underwater mines.
Using the Naval Academy's Oceanography Department Yard Patrol (YP) craft, penetrometers of varying diameters will be repeatedly dropped off the stern of the YP and allowed to free fall to the seabed. Several sites with differing soil parameters will be used. The data acquisition system on-board the YP will start recording accelerometer output before release and continually throughout the drop. By integrating the acceleration data, the velocity of the penetrometer can be obtained, and a second integration will yield the distance traveled. Using this experimental data and equations available in the Handbook for Marine Geotechnical Engineering, new values will be calculated for the strain rate factors of objects larger than three inches in diameter.
A computational analysis of the seabed penetration problem will also be conducted using the LS-DYNA finite element analysis (FEA) code. LS DYNA® will be used to model the experiments, and then the model predictions will be compared to experimental results. If the model shows reasonable agreement, then a parametric study will be conducted to further develop the empirical strain rate constants.
This research into sediment strain-rate dependence on penetrator diameter has the potential to significantly improve the Navy’s ability to predict embedment depth of objects placed-on or impacting the seabed. The experimental portion of the study will extend past published work by increasing object diameter, and the large-deformation finite element analysis will provide more understanding of the dynamic soil-structure interaction problem.
- 1/C Eric T. Regnier
- Major: Systems Engineering
- Title: Autonomous Swarm Actuation of a Disabled Vessel
- Advisor: Associate Professor Matthew G. Feemster, Weapons and Systems Engineering Department
- Advisor: Associate Professor Joel M. Esposito, Weapons and Systems Engineering Department Abstract
Autonomous Swarm Actuation of a Disabled Vessel
The primary focus of this research project is the investigation of the design, development, and implementation of a control system capable of coordinating the efforts of a swarm of autonomous tugboats with the aligned objective of maneuvering a disabled vessel along a desired trajectory.
In this project, "swarm" refers to a grouping of robots that work collaboratively to perform a task as a team, rather than one robot performing the task independently. For the swarm to approach a decentralized architecture (decentralized means that each tugboat is capable of making its own decisions) the robots must minimize the amount information transmitted to other swarm members, which is desirable since communication systems may be susceptible to failure and attack. There are drawbacks to decentralization however, as operational performance generally improves with increased information sharing.
In previous research, Trident Scholar Erik Smith designed three control strategies for the given scenario that analyzed operational performance under varying degrees of system knowledge and decentralization. However, Smith's control strategies were developed under two assumptions. The first assumption is that the tugs are arranged about the hull in opposing pair fashion (such that the axis of the thrust produced by each tugboat passes through the axis of its partner) and that the tugs are aware of their position relative to the boat's center of mass. The second assumption is that the tugs remain at a fixed incident angle to the hull of the boat. As a result, this project can be divided into three thrust areas: 1) the design, development, and verification of a control strategy that does not require the swarm tugboats to be restricted to an opposing pair arrangement while promoting positioning capabilities to the disabled marine vessel, 2) the minimization of data passing between swarm members, and 3) the construction of an open-water experimental test stand on which the developed controls will be tested. Metrics for each controller trial will include time to station, position error on station, and efficiency of movement to station.
- 1/C Mark G. Richard
- Major: Mechanical Engineering
- Title: Computational Modeling of Propeller Tip-vortex Impingement on Ship Rudders
- Advisor: Professor Karen A. Flack, Mechanical Engineering Department Abstract
Computational Modeling of Propeller Tip-vortex Impingement on Ship Rudders
In high speed marine vessels, surface pitting due to propeller and rudder cavitation can cause significant damage to both components, detracting from design life and performance. Sources of cavitation damage to ships’ rudders include surface cavitation, due to propeller induced swirl and rudder angle of attack, and impingement of propeller tip-vortex cavitation. Although surface cavitation can cause damage at high rudder angles, surface pitting is primarily a result of the collapsing of tip-vortex streams on the rudder surface. This experiment involves analysis of the interaction between these vortices and the rudder and will focus on reducing the effects of cavitation by using different hydrofoil shapes to alter the hydrodynamic characteristics of the flow over the rudder.
Experiments will be performed in a 12-inch water tunnel, simulating propeller tip vortex impingement on a rudder. Particle Image Velocimetry (PIV) will be used to evaluate the rudder flow field and to observe the influence of propeller tip-vortices, which will be useful in determining wake features, particularly tip vortex trajectory. Additionally, Computational Fluid Dynamics (CFD) will be used to simulate the same flow conditions as the water tunnel experiment. Once the CFD results are modified to match those of the PIV tests, flow field characteristics and rudder shape can be altered computationally to optimize rudder design. PIV water tunnel experiments will be conducted at the Pennsylvania State University Applied Research Laboratory during a summer internship and CFD computations will be performed at the U.S. Naval Academy using a cluster of parallel computer processors.
The goal of the project is to understand the flow field over the rudder, including propeller tip vortices, so that rudder modifications can be designed and developed to reduce tip vortex impingement. Minimizing rudder cavitation will extend service life, reduce corrosion maintenance, and maintain rudder performance, which will cause a decrease in operating cost.
- 1/C Michael L. Sapienza
- Major: Mechanical Engineering
- Title: Characterization of Railgun Material Behavior Under a High Compressive Strain Rate
- Advisor: Commander Lloyd P. Brown, USN, Mechanical Engineering Department Abstract
Characterization of Railgun Material Behavior Under a High Compressive Strain Rate
This research project proposes to combine expanding ring test data with experimental data gathered on a Split Hopkinson Bar to characterize the stress state and possible failure modes which proposed railgun materials experience during launch. The current-carrying conductors of a railgun experience immense changes in electro-thermal and magnetic conditions during projectile launch. Temperatures near the conductor melting point and stress near material failure may be achieved during the initial milliseconds of railgun activity. Little is known of these transient conditions on material properties because of the short duration of the launch event. However, such effects on material properties cannot be overlooked in the development of the railgun. The ability to accurately model system behavior is imperative as high tolerances are required in order for the railgun system to function properly.
The expanding ring test uses a thin specimen of railgun material surrounding a coil that is in turn expanded via an electrical pulse using a capacitor bank as a power supply. The specimen subsequently expands and fragments due to electromagnetic forces, as a current is induced in the specimen when the expanding coil is pulsed. The event is of such short duration that adiabatic heating occurs in the specimen, allowing for measurement of adiabatic thermal properties while experiencing high strain rates. Expanding ring tests will be a primary source of experimentation due to the ease with which the current, loading rate, and electromagnetic forces can be controlled.
A larger portion of research will focus on material samples subjected to a Split-Hopkinson Pressure Bar test to reveal behavior at very high rates of strain. While there is no common “Hopkinson” apparatus, the principles remain the same for its construction. A compressed gas launcher will fire a striker bar into an incident bar. The incident bar will send the compressive pulse through the sample. The sample will transfer the excess momentum into a momentum trap via a transmitted bar. Each bar will be of known modulus of elasticity and have strain gages to measure load as a function of time. Loading rate data shows a relationship between deformation of the sample and velocities and forces at the interfaces where the bars and sample are in contact. The data will characterize sample behavior under extreme dynamic strain conditions which may be correlated to events similar to those of the rail gun.
The Hopkinson tests will be correlated with the data from the expanding ring tests to evaluate variation in material properties, namely yield and tensile strength, as a function of strain rate. It is also anticipated that the expanding ring tests will create a higher strain rate than that of the Hopkinson bar, both of which are of a much higher rate than that of a conventional load frame operated at maximum test speed. Between the expanding ring test data and the Hopkinson bar test data, along with tabulated data for material properties from conventional load frame testing, the behavior of prototype railgun materials can be compared over a significant range of strain rates, enabling a more informed decision as to the proper choice for a railgun conducting rail material.
- 1/C Tucker F. Stachitas
- Major: Mechanical Engineering
- Title: Evaluation of the Aerial Radiological Dispersion and Identification Mapping System Using Hazards Prediction and Assessment Capability Software
- Advisor: Professor Martin E. Nelson, Mechanical Engineering Department
- Advisor: Professor Mark J. Harper, Mechanical Engineering Department Abstract
Evaluation of the Aerial Radiological Dispersion and Identification Mapping System Using Hazards Prediction and Assessment Capability Software
This project investigates the performance of the Aerial Radiological Dispersion and Identification Mapping System (ARDIMS) for use onboard the Fire Scout, a small unmanned helicopter with modular payload capacity of up to 600lbs. ARDIMS pods can be attached to the sponsons of the Fire Scout and flown over a radiological area such as that created by the detonation of a radiological dispersal device (RDD) or a small nuclear device.
The project uses the Hazard Prediction and Assessment Capability (HPAC) software package to analyze radiological dispersion. This program takes various user defined input conditions to analyze such effects as humidity, wind, and source radioisotopes. HPAC has many outputs, one of which is the ground level radioactivity concentration versus distance from the detonation. This output will be converted into a detector interaction rate using fundamental principles of radiation transport and interactions with matter. From this analysis, the project will evaluate the effects of different radioisotopes, explosive sizes, and environmental conditions.
This project will add to the growing body of knowledge on aerial radiological measurement and aid in the development of ARDIMS. Given the threat of nuclear terrorism in today’s world, this project could have a direct effect on national security by increasing in the ability of the United States to detect and respond to radiological incidents.
- 1/C Gerald E. Vineyard
- Major: Electrical Engineering
- Title: Characterization of a GTO Opening Switch in an Inductive Pulse Forming Network
- Advisor: Associate Professor John G. Ciezki, Electrical Engineering Department
- Advisor: Assistant Professor Thomas E. Salem, Electrical Engineering Department Abstract
Characterization of a GTO Opening Switch in an Inductive Pulse Forming Network
This research project involves an investigation of the current interruption capacity of Gate Turn Off Thyristors (GTOs). A series of GTO devices will be used with different gate drivers and protection circuits to interrupt different levels of current. The objective of this project is to determine if the gate driving circuitry of a GTO can be modified to optimize its current interruption capacity for use as an opening switch in an inductive pulse forming network.
This project will benefit the current research work that is being performed for the Navy railgun weapon systems. Significant research is being done to develop a pulse power system that can meet the energy requirements of the railgun weapon while being small enough to fit into the ship. Current research indicates that inductive pulse forming network could satisfy the “energy-density” requirements of a naval railgun system.
Unfortunately, inductive pulse forming networks require high-current opening switches to initiate the output current pulse. The opening switch interrupts the current that supplies energy to the inductor and causes the inductor to output that energy as a pulse of high current. It is important for the switch to rapidly interrupt the charging current in order to maximize the efficiency of the resulting current pulse. The challenge is to find a switching device that can achieve a fast turn-off time and tolerate the large charging current.
One promising type of switching device is known as a Gate Turn Off Thyristor (GTO); a GTO is a solid-state electronic switches that can be turned on and off with control current pulses. Several research projects have shown that some GTOs can be used in a pulse power system to interrupt currents that are significantly higher than their specified "maximum interruptible current." The research projects did not determine why the GTO’s could interrupt higher than rated currents.
This project will test a series of GTO’s to determine their ability to interrupt current in a pulse power system. The tests will determine if the different gate current pulses affect the maximum current that the switches can interrupt. Additionally, the project will characterize the voltage-current characteristics of the GTO’s to determine how the switches behave when used to interrupt higher than rated currents. Ultimately, this project will determine if the gate control circuitry can be modified to maximize the current interruption capacity of a gate turn off thyristor.
Division of Math and Science
- 1/C Sarah L. Catalano
- Major: Mathematics (Honors)
- Title: Zeta Functions and Their Relation to Formally Self Dual Codes
- Advisor: Professor W. David Joyner, Mathematics Department Abstract
Zeta Functions and Their Relation to Formally Self Dual Codes
This research project involves an investigation of error correcting codes. The safe and reliable transfer of information depends on coding theory. The problem of transferring dependable information is important and this research project attempts to continue incremental progress in this field. Specifically, the project will emphasize binary formally self dual codes.
In coding theory, a dual code is the code that is perpendicular to the original in the vector space. If a code is self dual, it is considered to be its own annihilator. Considerable work has been devoted to the study of self dual codes. Iwan M. Duursma has written numerous papers on the matter and the greater part of this project is centered on his ground breaking work. In 1999, Iwan M. Duursma defined the zeta function for a linear code as a generating function of its Hamming weight enumerator. The modest goal of Midn Catalano’s project is to go through Duursma’s papers and evaluate its relevance for formally self dual codes. Therefore, the research projects aims to extend Duursma’s work in Extremal Weight Enumerators and Ultraspherical Polynomials to formally self dual codes. More specifically, the project expands Duursma’s work in this paper to zeta functions of formally self dual codes of Type IV code.
The final and more ambitious goal of the project is to study the formulation for a Riemann Hypothesis analog. The unsolved Riemann hypothesis has been a mystery since Riemann’s work in the 1800’s. The search for an analog of linear codes arose in the 1990’s. This hypothesis deal with the nature of non-trivial zero’s for zeta functions. The applications of the Riemann Hypothesis for Zeta functions will be studied in this project.
This project has value because the study of error correcting code is relatively new and undeveloped. Profound advancement can be made in this field and is necessary for the transfer of reliable and safe information. The study of error codes performed in this research project is specifically related to reliable communications. This is especially pertinent to Naval Reactors as nuke power begins to rely more heavily on digital communications. The need for such communication to be reliable is paramount. Error correcting codes are vital to systems, such as nuclear reactors, that depend upon computers and cannot be allowed to mis-communicate. More knowledge of this topic is crucial to the overarching goals of the Navy. This is especially true if the Navy continues with its plans for unmanned ships. The military depends upon reliable, fault tolerant communication. This project aims to continue research in this pertinent field.
- 1/C Rachel A. Dougherty
- Major: Physics
- Title: Isotopic Abundance Information from Proton Induced Gamma-ray Emission Measurements
- Advisor: Professor Jeffrey R. Vanhoy, Physics Department Abstract
Isotopic Abundance Information from Proton Induced Gamma-ray Emission Measurements
Studying the chemical composition of materials can be accomplished through different techniques, including chemical and accelerator-based elemental analysis. The former is time-consuming, requiring lengthy handling of the sample. It ultimately results in the destruction of the sample itself - an unwanted consequence, especially when dealing with rare and expensive materials. The latter, on the other hand, keeps the sample intact and undamaged.
In some cases, it is useful to know not just the elemental makeup, but the isotopic composition of materials. Variations in isotopic abundances which deviate from "standard" abundances may be due to the following: sensitivity of chemical reaction rates to the isotopic mass of the reactants, sensitivity of physical processes (transport, crystallization, etc) to the isotopic composition, or possibly differences in radiation environment.
Measuring the γ-rays emitted from samples following proton bombardment, PIGE, (proton-induced gamma-ray emission) reveals information on the atomic nuclei. Since each nucleus has a unique structure, the measurement and study of the γ-rays can reveal both the particular isotopes present and their relative abundances. Study of these isotope-PIGE measurements provides information of the formation and evolution of earthly geological samples as well as meteorites.
Gamma-ray spectra will be measured following proton bombardment of (somewhat) standard samples. Two NIST-traceable isotopic standards are already available in the accelerator laboratory at the United States Naval Academy. The yields of γ-ray lines in the detector spectra will be stripped using common analysis routines. Conversion of detected yields to γ-ray production yields requires a detector efficiency calibration with existing 56Co, 60Co, 152Eu sources.
Typically PIGE analyses are performed with simple paper calculations, but the amount of information available from a complete spectrum is very rich and calls for more computing power than that provided with a pencil and paper. Unfolding the relative abundances is best done with a unified treatment not unlike the procedures used in optical molecular spectroscopy. Computer codes will be written to implement those techniques.
Proton-induced g-ray production cross-sections will be measured as a function of bombarding energy for the stable oxygen and magnesium isotopes. This data will be used to determine the optimum energies at which to search for variations in isotopic abundances in samples. Analysis codes will be developed to unfold the abundances from experimental γ-ray yields. The sensitivity of the technique to small variations in abundances will be analyzed.
- 1/C William Eucker IV
- Major: Physics
- Title: Room Temperature Ionic Liquids as Novel Sorbants for Submarine Atmosphere Purification
- Advisor: Associate Professor Paul C. Trulove, Chemistry Department
- Advisor: Associate Professor Paul T. Mikulski, Physics Department
- Advisor: Associate Professor Joseph J. Urban, Chemistry Department Abstract
Room Temperature Ionic Liquids as Novel Sorbants for Submarine Atmosphere Purification
This research project involves an investigation of the interaction of carbon dioxide (CO2) and selected room-temperature ionic liquids (RTILs). Raman spectroscopy and ab initio modeling will be performed on selected RTILs in contact with CO2 in the effort to discover how the gas interacts with the solvent.
Currently on board U.S. submarines, monoethanolamine (MEA) is used as the CO2 capture agent in scrubbing units. MEA is highly volatile, corrosive, physiologically toxic, foul-smelling, and requires replacement after approximately 1000 operational hours. A goal of the proposed project is to evaluate RTILs to replace MEA.
RTILs are salts (mixtures of cations and anions) that are liquid at room-temperature. Recent work has shown that gas solubilities in RTILs vary dramatically depending on the cation and anion that compose the RTIL. Tailoring the ion structures may therefore optimize the RTIL’s ability to dissolve CO2. Further, the CO2 solubility, negligible vapor pressure and high thermal stability of RTILs point to their potential application as CO2 scrubbing chemicals.
A combined experimental and computational effort will investigate the factors which govern the CO2 solubility mechanism. Initial studies will focus on six RTILs formed by the permutations of three anions: Hexafluorophosphate, tetrafluoroborate, bis(trifluoromethylsulfonyl)imide; and two cations: 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium.
In-situ variable-temperature Raman spectroscopy will be performed on the selected RTILs in equilibrium with atmospheres of different CO2 and N2 partial pressures. Raman spectroscopy is an optical technique capable of resolving molecular vibrations characteristic to inter-molecular interactions. The vibrational frequencies attributed to the RTIL and CO2 molecules are predicted to shift in response to the externally varied temperature and partial pressure of CO2. The competing solvation mechanisms and application operating conditions will be explored by systematically varying the temperature and gas composition. Experimental considerations include enabling requisite convective mass transport of gas to establish equilibrium and limiting the sample water content.
Ab initio computational modeling will be used to investigate the molecular pair interactions of the CO2 with a select RTIL cations and anions. Gaussian03 and Spartan’02 will be used to compute optimized geometries and vibrational frequencies. The computed Raman vibrational modes will be attributed, correlated, and analyzed.
The combined experimental and computational treatment will expand the current molecular-level understanding of the physical interactions which facilitate selective thermodynamic solvation of CO2 in various RTIL systems. The results will yield a quantitative rubric by which to choose an RTIL for use as a sorbant for submarine atmosphere purification.
- 1/C Michael E. Eyler
- Major: Physics
- Title: Time Delay and Microlensing Analysis of Lensed Quasar QJ0158-4325
- Advisor: Lieutenant Commander Christopher W. Morgan, USNR, Physics Department Abstract
Time Delay and Microlensing Analysis of Lensed Quasar QJ0158-4325
This project is concerned with the gravitational lensing of light from the distant quasar QJ0158-4325 by a massive foreground galaxy. In such systems, the galaxy’s gravity causes multiple images of the quasar to appear to the observer. As the quasar undergoes brightness variations, gravitational slowing and differences in light travel path length cause time delays between the appearance of the intrinsic variability in each image.
These time delays depend on both the expansion rate of the universe and the distribution of matter in the lens galaxy. Time delay measurements are therefore useful for measuring the Hubble constant H0, a number whose value parameterizes the expansion rate, as well as the distribution of so-called “dark matter” in the lens galaxy. This project’s primary goal is to determine the time delay of QJ0158-4325 and to make these measurements simultaneously.
The case of QJ0158-4325 is complicated by “microlensing” of the quasar light by stars in the lens galaxy. Stars lack the gravitational potential to produce multiple observable images, but they do cause uncorrelated variability in the image fluxes as they pass in front of the quasar. Such variability must be eliminated in order to measure a time delay. A series of physical models for the lens galaxy will be created to accurately model and remove the signal from microlensing. This analysis will permit a time delay measurement and yield estimates of other physically interesting quantities, including the average stellar mass in the lens galaxy and the size of the quasar accretion disk.
This project will utilize over three years of flux monitoring data for QJ0158-4325. The microlensing extraction will be performed using a Monte Carlo technique in which a series of microlensing simulations will be run using various combinations of physical parameters and testing a range of time delays. The goodness-of-fit of the simulated light curves to the data will then be used in a Bayesian analysis to determine a most likely value for the time delay. The same analysis will be applied to estimate other physically interesting parameters, and the time delay will be compared to that generated by a series of mass models to determine the distribution of matter in the lens galaxy.
- 1/C Austin G. Hancock
- Major: Quantitative Economics
- Title: Development of an Assessment Tool for Analyzing Electronic Warfare Success in an Urban Environment
- Advisor: Commander David R. Spoerl, USN, Mathematics Department Abstract
Development of an Assessment Tool for Analyzing Electronic Warfare Success in an Urban Environment
This research project involves an investigation of the statistical methods useful for analyzing an electronic warfare engagement. The study involves representing an air defense system and corresponding target through a series of architectural frameworks that capture the functional aspects of interest. The primary factors can be extracted and their interactions and behaviors described through a set of discrete parameters. Preliminary analysis will be used to determine which factors are most influential in predicting the success or failure of the engagement. Once this is accomplished, response data will be collected that reflects how effective the system performs under a range of system attributes. This information will be then analyzed using methods from design of experiments and operations research to determine the sensitivity of the system to different values. The research is also concerned with the importance of maintaining communication integrity in the integrated air defense system. Since the radar and strike site will be realistically affected by the stochastic nature of information and disinformation, the model will account for how information flows impact the total functionality. Disciplines that will be explored go beyond statistics and optimization to include information theory, game theory, and systems engineering.
Extension of this research will be executed in concert with The Johns Hopkins University Applied Physics Laboratory. This simulation, as well as the flow diagrams, should be sufficiently versatile to allow for evaluation in multiple environments. The necessity of developing a simulation model is that it will provide otherwise impossible analysis of both the independent contribution of entities as well as their interactions. With sufficient repetition, the model should provide an unbiased indicator of electronic warfare lethality. The goal of the research is to optimize the characteristics of a radar system and corresponding strike package to satisfy a predetermined measure of effectiveness.
- 1/C Evan P. Seyfried
- Major: Physics
- Title: Study of Severely Neutron-deficient Nuclei in the Actinide Series
- Advisor: Associate Professor Daryl J. Hartley, Physics Department Abstract
Study of Severely Neutron-deficient Nuclei in the Actinide Series
This project is a study of the nuclear structure of isotopes of Francium, Radon and Astatine (that are neutron-deficient) through analysis of gamma ray emission from excited states. There is very little known about these neutron-deficient Actinide nuclei. The isotopes are very rare, difficult to create and have not been studied thoroughly. They provide an opportunity to test calculations and predictions of the shell model of the nucleus.
Via a nuclear fusion evaporation reaction of a 28Si ion beam on a 181Ta target, highly excited 209Fr nuclei are produced. These energetic nuclei lose their energy by radioactive decay, most often emitting neutrons and alpha particles, then releasing an idiosyncratic series of gamma-rays. The characteristic energy levels that the nuclei decay through toward their ground states are a useful tool in determining nuclear structure.
A Washington University research team, using their HERCULES residue/fragment detector, has provided data far cleaner than previously possible; what remains is to take the large matrices of gamma-gamma coincidences and establish energy level schemes, complete with corresponding total angular momentum and parity states.
The goal of this project is to process the matrices, and piece together sequential decay bands using coincidence gating of same-energy gamma-rays. This process will be used within the same data set to extract the excited state energies for a number of nuclei in the Actinide region: Francium, Radon, and Astatine. Shell model calculations will be performed to yield expectation values for the observed energy bands.
This project is important because for some nuclei created in the reaction, no one has ever measured the excited states in the neutron-deficient region, or only a few lower level energy states are known. The results of this course of analysis will add to the general knowledge of the properties of exotic nuclides.
- 1/C Jeffrey E. Vandenengel
- Major: Chemistry
- Title: The Optimization of Tobrymycin Beacon Aptamers
- Advisor: Assistant Professor Daniel P. Morse, Chemistry Department Abstract
The Optimization of Tobrymycin Beacon Aptamers
In this research project, work will be undertaken to improve the method for in vitro selection of beacon aptamers. An aptamer is any molecule that binds to and aids in the quantification of any specific target molecule. They are used in countless areas of chemistry, and more and more uses are being found for them. One specific type is the beacon aptamer, which is an RNA sequence that undergoes a conformational change when it binds to a specific molecule. Attached to the molecule is a fluorophore and a quencher, which are molecules that release and absorb light, respectively. When the ligand, or target molecule, is not bound then the fluorophore and quencher are close to each other, allowing theoretically little to no light to escape. When the ligand binds it forces the beacon aptamer to change shape, causing the quencher to move away from the fluorophore, allowing the amount of fluorescence and thus amount of ligand present to be measured.
The primary focus of this research will be to find an RNA sequence that can be converted into a functional tobramycin beacon aptamer. Rather than starting with a totally random collection of RNAs, a new selection will be performed starting with a pool of RNAs that are all closely related to one of the previously selected marginally functioning tobramycin beacon aptamers. Additional sequence variants will be produced during the selection by performing the amplification step under conditions that reduce the fidelity of replication. Improved variants will be selected by increasing the "selection pressure" in various ways, including reducing the tobramycin concentration and the elution time.
Beacon aptamers can be used for a wide array of applications. They could be used by the military to detect chemical or biological warfare agents. They could also be used in medicine for diagnostic purposes or by environmental scientists to study the amount of pollutants or toxins in a certain region. Of particular interest are their potential ability to quantify specific molecules in cells and within the body. There is great interest in developing methods for the efficient production of functional beacon aptamers, something that has proven difficult to date with the currently employed techniques.