Trident Scholar Abstracts 1998
In this project, a computer-based methodology was developed, using the Monte Carlo N-Particle transport code, for the optimization of the photon response in a LiF thermoluminescent dosimeter.
The current dosimeter used by the Naval Dosimetry Center will soon be replaced by an improved system due to increasingly strict government standards in dosimetry. Research has been done on the thermoluminescent material and on the reading algorithm, but little research had been done on the card holder. This work accomplished in this project contributed to the new system by optimizing the filter system of the card holder for photon energy response.
First, a model was created to calculate the energy deposited in the current dosimeter for various NIST beams. These calculations were correlated with experimental data from NIST. In order to increase the accuracy of the model, further energy deposition calculations were made using the MCNP code. Many significant results came from this modeling. For example, the model which correlated the most closely with the experimental data did not include electron transport, a physical process that would otherwise be included.
Using this MCNP model, the Navy's proposed card holder is being improved by changing filter materials and thicknesses. It has been determined that a combination of copper and tin performed better than other materials. Also, increasing the copper filter thickness by 20 times and doubling the tin filter thickness over the original design created an improved photon energy discrimination response. Experiments were performed with this improved card holder at Armstrong Laboratories at Brooks Air Force Base, Texas. These results also correlated well with the model.
This research performed in this project successfully improved the photon response of the Navy's dosimeter. Studies are now being conducted to implement these improvements in the Navy's system.
The purpose of this project was to study porpoising, one of the most common forms of dynamic instability found in planing boats. In descriptive terms, it is a coupled oscillation in pitch and heave that occurs in relatively calm water. These oscillations can be divergent in amplitude, leading to loss of control, injury to occupants or damage to the craft.
The mechanics of porpoising have been studied sporadically from theoretical and experimental perspectives for many years. Studies by Perring (1933), Savitsky (1950 through 1976), Day and Haag (1953), Martin (1978), and others have shown that the inception of porpoising is influenced by displacement, center of gravity location, and various hull characteristics such as deadrise and beam.
Until now, Day & Haag's thesis provided the only systematic test results concerning the porpoising stability limits of planing craft. Although the Day and Haag model tests were brilliantly executed and thoroughly reported, many users of this data are not aware of the size of the models tested. The average beam of the three tiny prismatic hulls was 3.8 inches. As a starting point, these tests were recreated using a series of three hard-chined prismatic planing hullforms approximately five times larger. The tests included hulls with higher deadrise angles, more typical of craft now employed for high-speed military purposes. Two models of actual full scale craft, complete with performance enhancing features including lifting strakes, trim tabs and variable drive angle were tested. The effects of these additions were found to have a profound effect upon the conditions at the inception of porpoising.
Established planing hull analysis methods were augmented with techniques developed during the course of the study to provide a basis from which to design and outfit high-speed, heavily laden planing hulls with respect to porpoising stability.
This project demonstrates the use of capillary electrophoresis as an improvement to existing methods of analysis for carbon monoxide in hemoglobin.
Hemoglobin is the protein found in blood that is responsible for the transport of oxygen, carbon dioxide, and carbon monoxide (CO) throughout the body. Current methods for detecting concentrations of CO in the human body are CO-oximetry, tonometry, and head space gas chromatography which involve lengthy sample manipulation followed by spectroscopic, saturation, or gas displacement measurements. These methods are time consuming and technically difficult because of the many manipulations they require.
Capillary electrophoresis (CE) is presented as a faster and easier method to quantify CO in hemoglobin. CE is an extremely efficient separation technique in which molecules, under the influence of an electric field, travel through a narrow-bore capillary tube and are separated based on differences in mass, charge, or shape.
Several steps towards the development of a CE procedure to detect CO in blood have been completed. The first step of this analysis involved isolating heme, the portion of the hemoglobin molecule where CO binding takes place, from the rest of the hemoglobin molecule. Mixtures of reduced (containing no gas molecules) heme and CO-heme were successfully isolated from hemoglobin standards.
In order to quantify CO in heme, it is important to separate CO-heme from reduced heme. Initially, this separation was accomplished using CE on hemoglobin standards. Finally, heme and CO-heme were isolated from blood samples of accident victims and analyzed using CE. A difference in the CO-heme signals from blood samples known to contain fatal and non-fatal levels of CO was observed. Further work towards actually quantifying CO in blood by CE is the next logical step in this multi-phase project.
This research involved the design and development of a physics knowledge base, which allows an intelligent tutoring system (ANDES) to more effectively assist students in physics problem-solving.
ANDES is an Office of Naval Research funded collaborative effort between the U. S. Naval Academy and the Learning Research and Development Center at the University of Pittsburgh. The system tutors Newtonian physics via coached problem-solving, a method of teaching cognitive skills where the tutor and the student work together to solve problems.
The knowledge base developed in this project provides the physics backbone to the rest of the tutoring system, by generating the necessary equations and solution graphs to solve the selected angular motion physics problems. These mathematical outputs are used by other ANDES components to provide help to the students in a variety of ways. In order for ANDES to be an effective tutoring system, the knowledge base developed had to fulfill certain criteria. It needed to model a teacher's approach to problem solving, using planning and decision-making strategies to find the solution path efficiently. It also had to be robust enough to generate several solution paths for problems that have more than one possible solution method.
Since this research was the first attempt to develop a knowledge base on the angular motion subject matter of physics, encoding these concepts presented unique challenges.. For example, the concept of normal force which is easily understood in the classic "object on top of a surface" problem becomes more difficult in the classic "roller coaster at the top of a loop" problem. However, both visualizations had to be modeled by the same implementation. The knowledge base designed and developed in this project successfully accomplished this modeling, and it is presently being incorporated into the larger ANDES project.
This study focused on very shallow features of the most recent Holocene channels in the mid Chesapeake Bay near Annapolis, MD, and west of Kent Island. The study used two sonar systems, a side-scan sonar to create a mosaic showing bottom topography and surface sediment characteristics, and a chirped subbottom profiler which penetrated up to 10 m into the sediments to reveal the distribution and characteristics of sediment layering.
Several different channels have north-south orientations, at depths between 1.5 m and 10 m below the sediment/water interface. Two strong sub-bottom returns separate three main layers. Shallow layer A has an average thickness of 2 m, and is characterized by smooth regular returns indicative of homogenous sediment. Intermediate layer B has an average thickness of 9 m, and contains many faint sub-bottom layers. Deep layer C extends below the strong return that marks the bottom of layer B. It also contains several strong returns, but is not well imaged due to limited return strength.
Analysis of the side-scan data indicates the orientation of the subbottom layering tends to follow the general bottom surface bathymetry and orientation of the present channel. Both sidescan and subbottom data reflect recent sediment deposition. The location and orientation of the subbottom layers show areas of sedimentation, while side-scan sonar data mosaics over the area help illustrate sediment fluxes.
Sedimentation in the study area is approximately 0.05 cm/yr to 0.075 cm/yr. This assumes the deepest subbottom return separating layers B and C represents the Cape Charles paleochannel (18ka) and uses the measured layer thicknesses.
This project investigated the possibility of constructing and characterizing a tunable light source from a laser diode and a fiber Bragg grating.
Optical technology has matured in the last century to the point where it can be used to construct dynamic systems such as circuitry or complex research instruments. Like electronic systems, these new optical systems can be used in a wide number of fields, from environmental sensing to rudimentary computation. In each of these applications, optical components could benefit from an internal, tunable source. Much like the superheterodyne in an FM tuner, a miniature, tunable optical source provides the foundation for a complex, dynamic, fiber optic communications network. In addition, precision tunable light sources have applications in fundamental research, including optical amplifier studies, and high resolution spectroscopy.
In this work, we constructed and characterized a tunable laser light source. It has a central wavelength of 683nm and a bandwidth less than one twentieth of a nanometer. It is tunable over a range greater than five nanometers. Although similar performance is obtained from existing tunable lasers, in this project the tunable laser was constructed using a semiconductor diode and a fiber grating. These components represent the very latest developments in optical technology. Their combined application is pointed to by industry and researchers as a fundamental step in the development of a vast, new field of technology.
This project demonstrated that magnetic bearings can be used as an actuator in an active sound control system, reducing tonal noise emissions of a motor and fan blade assembly.
It is often desirable to control the noise emissions of rotating machinery, whether in industry, either for safety or aesthetic purposes, or in military applications, for stealth. Passive dampening materials and barriers are effective and practical for reducing high frequency sound, but the bulk and weight necessary in such structures to block low frequency noise makes them impractical in many situations. Active sound control--the cancellation of one noise by transmission of another, "secondary," sound wave--provides a viable alternative for reducing low frequency noise.
This project investigated many aspects of active sound control, including the acoustic mechanisms of sound cancellation and various computer algorithms used in sound control. The primary focus of the project, however, was the method of producing the secondary sound. Magnetic bearings, which can support a rotating shaft without contact, were used to vibrate a shaft and propeller at a certain frequency, producing the secondary sound in an active noise control system. The bearings were controlled by a digital signal processor, which adjusted the phase and amplitude of the secondary sound. The signal processing algorithm adapted itself based on noise level feedback from a microphone to produce the greatest noise reduction possible.
The U.S. Navy has already shown great interest in magnetic bearings, and this project has demonstrated a significant additional benefit to be gained from their use aboard ships.