Hope College Physics and Engineering
Research Projects
Summer 2007
| Structural Engineering | Interdisciplinary nuclear science | Blast Damage |
| Nonlinear systems control | Nuclear physics | |
| Chemical property modeling | Astrophysics | Cryogenics |
| Dr. Miguel Abrahantes | Dr. Paul DeYoung | Dr. Mike Misovich |
| Dr. Jeff Brown | Dr. Peter Gonthier | Dr. Graham Peaslee |
| Dr. Steven Remillard | Dr. John Krupczak | Dr. Roger Veldman |
This project is in collaboration with the NASA/Goddard Space Flight Center in Maryland. Engineers at Goddard are designing a more ambitious rover. It does not have wheels. Instead, it looks like a shape-changing jungle gym, with trusses that lengthen and shorten. It is a complicated type of movement to explain, and is best demonstrated in video (http://ants.gsfc.nasa.gov/). This robotic structure is composed of self-similar parts, struts, and nodes, allowing the robots to be assembled in the field into a variety of tetrahedral configurations. The Goddard team is investigating different approaches for the locomotion control of this structure. Our team at Hope College is assisting the NASA group with the design of control strategies for autonomous gaits or ways to "walk". This design involves the chorographic shape-changing movement of the structure. Since the structure is over constrained, the control needs a precise geometrical definition of the shape-changing movement. Students will work to obtain this geometrical description of the structure to be used as a reference for the control strategy. It will start from a simple one tetrahedral robot and build up the number of tetrahedral to 12. The control strategies will be implemented using a simulating robot model based on Matlab/Simulink/SimMechanics software.
This research involves strengthening existing civil infrastructure using fiber reinforced polymer (FRP) composites. FRP composites are currently applied to bridges, buildings or other reinforced concrete structures in order to provide additional load carrying capacity. The application procedure for FRP strengthening systems is very similar to applying wallpaper: dry fibers (typically carbon) are saturated on-site and applied to the surface of the concrete to the FRP composite via shear stress across the bond line. Serious problems can arise if these systems are not installed properly and air bubbles are present between the FRP and the concrete.
One method for determining whether or not an FRP system is properly bonded to concrete involves thermal imaging. The general concept behind the technique is to apply heat to the surface of an FRP composite using standard IR heat lamps. This will result in a thermal front that travels from the surface into the concrete substrate. If any defects or air voids are present at the FRP/concrete interface, the heat flow will be interrupted and a "hot-spot" will occur on the surface. This hot-spot can be detected using an infrared camera.
Specific objectives for this summer position are aimed at applying the infrared thermography technique to investigate the criticality of defects in FRP systems applied to reinforced concrete. Several small-scale reinforced concrete beams will be constructed and FRP composites will be used to strengthen these beams in flexure. Defects will be implanted at the FRP/concrete interface and the beams will be subjected to fatigue loading. Infrared thermography inspections will be conducted at various stages in the fatigue loading process. The purpose of these inspections will be to determine if the implanted defects adversely affect the fatigue life of the FRP system.
The student will be responsible for the design and construction of the small-scale beams, applications of the FRP systems, and subsequent fatigue loading experiments. The student will also gain experience using a state of the art thermal imaging system. Various data analysis techniques for processing thermal imaging data will also be investigated.
TBD
As the ability to accelerate exotic radioactive nuclear beams has developed at different accelerators around the country, we have developed an ambitious program in this area of study using the accelerators at the National Superconducting Cyclotron at Michigan State University and the Nuclear Structure Laboratory at the University of Notre Dame. Using the TwinSol facility at ND, the effect of the neutron skin of the 6He nucleus on reaction dynamics near the Coulomb barrier is studied. We have found that this skin enhances the probability of fusion near the barrier. Our present studies aim to understand the interplay between one-neutron transfer, two-neutron transfer, and projectile breakup mechanisms and how the neutron-skin structure of this nucleus impacts these interactions. The current focus is to understand the breakup of 6He as it passes through a target. This work utilizes two large-area (5ft by 5ft in 8 segments) plastic, position-sensitive neutron detectors that were constructed by the Hope Nuclear Group. In collaboration with the NSCL, Hope College was one of nine schools that constructed the MoNA detector, a 144 element neutron detector (4 tons!). With this device we study the structure of nuclei far from stability such as 25O or 13Be. The Nuclear Group has been involved in most of the experiments done with MoNA. Students working on these projects will be involved in detector construction, running experiments, analyzing data (including such things as detector calibration, particle identification, and gating), modeling, and presenting results.
We explore the emission of gamma rays from the magnetospheres of neutron stars from a theoretical approach. The emission of gamma rays is initiated from the acceleration of charges, electrons and positrons, along magnetic field lines that have a parallel electric field. There are two theories that describe the location and geometry of the acceleration and subsequent emission process. The polar cap model locates the acceleration zone right above the stellar surface at the magnetic poles, while the outer gap model describes the acceleration far out in the magnetosphere near the light cylinder where the speed of the co-rotating magnetic field lines approach the speed of light. The geometries of the beams predicted by these two models are quite distinct. However, since there are only eight, possibly ten, known gamma-ray pulsars, the issue is not quite settled. The gamma-ray telescopes, AGILE and GLAST, are scheduled for launch during 2007 and will discover many new gamma-ray pulsars. In this research project, we also study the radio emission from neutron stars. There are nearly two thousand radio pulsars known. While radio pulsars have been known since the mid-sixties, the mechanism of emission has not been understood. Therefore, our understanding of radio emission is purely from an empirical or phenomenological approach. Radio astronomers generally agree that the radio emission originates along magnetic field lines above the stellar surface. We agree with those astronomers who describe a radio core beam that is center along the magnetic pole near the surface, maybe at similar altitudes above the surface where the gamma-ray emission occurs. In addition, typically the radio pulse profiles indicate the presence of a conal beam being emitted from a ring-shape region at higher altitudes than the region of the core emission. Using the characteristics of radio pulsars with profiles containing three peaks, we attempt to improve the understanding of the characteristics of the core and cone beams and how the intensity of these beams depends on observed quantities like the pulsar period and period derivative. We have developed a computer code that simulates the characteristics of both radio and gamma-ray emission predicting the number of radio and gamma-ray pulsars observed by various radio surveys and gamma-ray instruments like EGRET, AGILE and GLAST. We believe that the studies of the correlations of the radio and gamma-ray pulse profiles will provide a framework to differentiate between the competing pulsar models. A second area of investigation in this project involves an aspect of the microphysics in the neutron star magnetosphere, where soft thermal X-rays from the stellar surface undergo inverse Compton scattering from relativistic electrons accelerated along magnetic field lines above the polar cap. We seek to develop a mathematical framework that is useful to astrophysicists to describe inverse Compton scattering in very strong magnetic fields. We will develop analytic expressions for the cross section in the highly supercritical fields associated with soft gamma-ray repeaters and anomalous X-ray pulsars, a class of pulsars known as magnetars. These expressions will be useful to magnetar modelers who are currently using Compton scattering cross sections that do not consider the effects of the strong magnetic field environment.
Working with Ahmed Sidi-Yeklef of Brookhaven National Laboratories, we will contribute to the RHIC Refrigeration System Power Reduction and Upgrade Phase III. Cryogenic systems inevitably include regions of two-phase liquid-gas flows. Heat flux to these regions can lead to unstable or oscillating behavior. System design seeks to conservatively avoid the impact of two-phase flows on system operation. However overall efficiency decreases and power consumption increases as a result. The ability to accurately model two-phase flow and transient behavior in large-scale cryogenic systems affords the potential of improved efficiency and reduced operating expense. This analysis combines fundamental principles of fluid mechanics, heat transfer, and thermodynamics with numerical analysis and computer simulation and is accessible to undergraduate students.
In chemical process design, engineers need general methods for predicting physical properties of various substances as both liquids and vapors. Chemical engineers commonly use cubic equations of state such as Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR). In this work, students will use common equations of state to predict vapor-liquid phase equilibrium and apply mathematical methods to generate data for physical properties from these equations. Mathematical principles of elementary calculus and elementary statistics will be studied and applied; specifically, multivariable series expansions, and linear/nonlinear least squares regression. Students participating in the research will be expected to have taken one year of calculus; or other coursework in math, chemistry, engineering, or computer science may be helpful but is not required of applicants. The goal of this work will be to generate relatively simple, yet general, equations to accurately predict physical properties.
Recent results have included a series approximation for the vapor pressure and phase densities predicted by the PR equation at moderate to high pressures; a series approximation for volume change and enthalpy change of vaporization predicted by the SRK and PR equations from low to high pressures; an improved approach for vapor pressures predicted by the SRK equation at moderate pressures; an asymptotic relationship for SRK vapor pressures at low temperatures; and a method for generalizing Antoine vapor pressure constants from the SRK equation.
Some current and upcoming research includes developing a technique for "tuning" the series method to converge well in a specific temperature range; applying the method to more complex cubic equations used in practice and simulation software, such as the Stryjek/Vidal variant of the PR equation or the Twu-Sim-Tassone (TST) equation; generalization or improvement of simpel estimation methods like Watson's correlation for heat of vaporization or the Rackett equation for liquid density; investigating approaches for applying the series method or alterntive methods with techniques like volume translation or lattice fluid equations that show proper scaling behavior at the critical point: and a generalization of the series method for predicting phase behavior of mixtures.
Hope College has its own 1.7 MV Pelletron tandem accelerator with a nuclear microprobe in the Hope Ion Beam Analysis Laboratory (HIBAL). With this device some students conduct environmental science research projects that utilize nuclear physics techniques to measure metal contaminants in lake sediments and soils. Particle-Induced X-ray Emission (PIXE) spectrometry is used for rapid assays of dried lake sediment samples where one can determine total metal content for most metals of interest in roughly one third the time of traditional wet chemistry acid-digestion techniques. We also collaborate with a member of the geology department to understand the provenance of West Michigan sand dunes using trace element analysis of sand. (The beam spot of the microprobe is significantly smaller than a single sand grain so a PIXE analysis of individual mineral constituents within the sand grain can be done.) Work also continues to understand the origin and extent of metal and nutrient contamination of lake sediment in various West Michigan lakes using 210Pb radiodating and PIXE analysis of sediment cores.
Much of the work in condensed matter physics involves the production of thin
conducting or semiconducting films on Si or sapphire substrates. With the
nuclear technique Rutherford Backscattering Spectroscopy (RBS), it is possible
to quantify
the thickness and composition of the thin layers making up condensed matter
samples. This technique can even be applied when the sample consists of multiple
thin layers (such as in anti-reflective coatings). We currently have on-going
collaborations with researchers here at Hope College, at the University of
Notre Dame, and a local company to study and characterize their films.
Another HIBAL opportunity for research students in physics with a biochemistry
background will be the continuation of a project to develop an ion beam analysis
technique utilizing energy-loss measurements of light charged particles passing
through a dried electrophoresis gel to obtain quantitative information about
protein distribution in the gels. This energy-loss measurement could provide
the first quantitative and reproducible measure of how much protein is in
which gel electrophoresis location. Combined with PIXE spectrometry it might
also
lead to a reliable quantitative method to ascertain metal ion stoichiometry
in proteins.
Lastly, we are developing the tools and techniques to examine
crime scene evidence. Primarily, the focus of the research done to date has
been to develop
the methodology
to reliably and non-destructively compare various glass samples and draw
conclusions about their similar or different origins with PIXE techniques.
We hope to extend
to other materials such as paints.
Since the tragic bombing of Pan Am flight 103 over Lockerbie, Scotland in 1988, significant research has been devoted to improving commercial aircraft safety against the threat of on-board explosions. These efforts are intended to determine the effects of explosions on aircraft structures and to propose design changes to increase the resistance of airframes to internal blasts. One important aspect of this research is to determine the effects of lightweight lining materials on minimizing fuselage blast damage.
This research project will utilize transient finite element analysis (FEA) to simulate the explosive loading on a pre-pressurized structure. For the FEA model, a flat aluminum plate with riveted stringer reinforcements will be used to represent a portion of a commercial aircraft fuselage. The FEA numerical model will be used to determine the effects of lining materials on deformation and damage of the plate under various blast loading scenarios. Additionally, the effects of blast loading on reinforced plates will be investigated experimentally. For this purpose, bare spherical charges of the explosive material, C4, will be detonated at fixed distances from aluminum test panels.
Students involved in this research will gain valuable experience using a sophisticated engineering software code to analyze the dynamic response of a structure under blast pressure loading. Additionally, the experimental work will give students an opportunity to design, fabricate, and utilize a test apparatus and to compare experimental and numerical results.