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Undergraduate Physics at The Ohio State University

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Undergraduate Research in the Department of Physics

Every year physics students present their research at the Ohio State University Denman Research Forum. Poster titles and research abstracts of some physics students who presented at the forum are shown below. To get a larger view of a student's poster, click the picture to the right of the abstract.

Presenters at the 2008 Denman Research Forum:

Presenter: David Albani
Title: Constrained Positron Flight Range in PET Imaging via Strong Magnetic Fields
Advisor: Klaus Honscheid
Department: Physics
Abstract:
    Positron Emission Tomography (PET) is a noninvasive imaging technology that has found use in clinical research and medical diagnostics. This imaging technique provides insight into metabolic processes such as disease evolution and the effect of pharmaceutical treatment on a subject. PET imaging works through the injection of a radioactive tracer into a host. Due to differences in metabolic rates, the tracer tends to accumulate more in cancerous cells than in healthy cells. Positrons emitted from the radioactive tracer travel a net range related to their initial energy and ultimately annihilate with an electron in the patient's body, creating a pair of photons traveling in opposite directions. Photodetectors detect the two emitted photons in coincidence. Utilizing reconstruction algorithms produces an image of the annihilation positions. Current methods permit commercial PET scanners to achieve resolution in the 1-2mm range. Due to the size of subjects used in small animal PET and their smaller organ systems, there exists the demand for resolution in the sub-millimeter regime. We have developed a small animal PET prototype utilizing silicon pad detectors with a measured spatial resolution of 0.7mm FWHM. At these sub-millimeter resolutions the range of positron flight is the ultimate limit to the resolution. In lower-energy isotopes this is not problematic, as the emitted positrons tend to travel very short distances before annihilation. This is true of more commonly used radioisotopes such as F-18 (635 keV maximum emitted positron energy). PET imaging with the use of novel isotopes of higher energy, such as Tc-94m (2470 keV maximum positron energy), exhibit significant blurring due to the longer travel distance of the emitted positrons. The presence of a strong magnetic field confines the flight of higher energy positrons in the direction transverse to the applied magnetic field. This makes it possible to both use these high-energy tracers and achieve sub-millimeter resolution. I have performed preliminary simulations of scanning events to predict the effects of the magnetic field on resolution. In the simulation I have tested sources of various sizes and energies implanted in environments with a range of static magnetic field strengths. The simulation results confirm that strong magnetic fields can greatly reduce the positron's range transverse to the applied magnetic field, thus making it possible to use higher energy positron emitters and still achieve high resolution images. In collaboration with the Department of Physics and the Ohio State University Medical School we have measured the reduction of the positron range for various radioisotopes of interest. This was accomplished by embedding our small animal PET prototype into the Medical School's large bore 7 Tesla MRI magnet. The experimental data strongly agrees with the simulation. To explore the system further I have performed simulations that analyze the effects of varying radioisotope position between the detectors. As a precursor to developing new scanners, I shall also adjust the detector spacing in simulation and examine the associated change in resolution.
Presenter: Megan Comins
Title: Systematic Errors in Black Hole Mass Measurement Using Reverberation Mapping
Advisor: Bradley Peterson
Department: Astronomy
Abstract:
    Active galactic nuclei (AGNs) are extremely energetic central regions of galaxies whose brightness cannot be attributed to stars alone. A typical AGN emits at least the same amount of energy that is emitted by an entire galaxy of stars, but in a much smaller volume. The basic paradigmatic model of an AGN is a dense gaseous disk through which matter is accreting onto a central supermassive black hole. This is surrounded by a region of relatively dense broad-line emitting clouds and then, further out, a region of relatively low-density narrow-line emitting clouds, known as the broad-line region (BLR) and narrow-line region (NLR), respectively. The disk is adding mass to the black hole, and in the process releasing radiant energy; this region is often referred to as the "central engine". The BLR is relatively near to the central engine, and it is thus a useful probe of this central region. One technique used to explore the BLR is reverberation mapping, which can reveal the structure and kinematics of the emission-line gas. The goal of this project is to explore how a measurement of the black hole mass, using reverberation mapping, within an AGN changes due to systematic effects inherent in using both a wind-based AGN model, as well as combination wind-disk model. This aim is to address two specific questions. First, how does the black hole mass measurement change when we characterize such a region by only two numbers that characterize the velocity dispersion of the emitting gas and the mean reverberation response time? The BLR is a complex region and we aim to determine how much information one loses through a simplified characterization. Second, how does the geometry of the wind affect the measurement of the black hole mass? Specifically, we explored the effects of changing the opening angle of a conical wind and its inclination with respect to an Earth-based observer. These questions are important to help discern the structure of the BLR. This model will help to gather intuition about how the geometry and kinematics of the BLR affect a black hole mass measurement obtained through reverberation mapping.

Presenter: Thomas Henighan
Title: Magnetic Arrays and Transport of Bio-Functionalized Particles
Advisor: Ratnasingham Sooryakumar
Department: Physics
Abstract:
    Micron- and nano-sized magnetic particles are useful in the field of medical research because of the ability to attach cells, viruses and DNA molecules to them. Such tethered magnetic particles could provide an important route to manipulate and maneuver biological molecules. Due to the high selectivity of magnetic separation methods, such functionalized magnetic particles are also finding uses in microfluidic device applications. Our goal is to create a platform suitable to trap and transport magnetic particles along predetermined pathways. We have investigated using ultra thin (~50 nm) films of a magnetically soft ferromagnetic alloy of iron-cobalt (FeCo) and selectively patterning them to form the basic scaffold of our platform. Through careful design we create structural elements whose magnetic properties can be tuned when placed in an external magnetic field. Depending on the shape of the patterned elements, their magnetization aligns like tiny bar magnets. By selecting the configuration of the elements and manipulating the external field, we trap and move the magnetic particles in a controlled way. We will present results from a series of elliptical-shaped thin FeCo disks with an aspect ratio of (3:1). The patterns were chosen based on simulations run on an available program which models the magnetic domains in specific structures in the presence of external magnetic fields. The ellipses we fabricated were oriented at right angles and separated from each other so that the magnetic particles jump from one ellipse to the next when placed in a rotating field. The ellipses were created by photolithography techniques which involved coating a substrate with a layer of electron-beam resistive material and writing the desired pattern with electron beams. In conjunction with a developing process, the resistive material was then removed enabling the FeCo to be deposited to produce the desired pattern. We observe that the magnetic particles are attracted to the ellipses through the magnetic fields they create. In response to the rotating external magnetic field, the trapped particle ?walk? around the edge of the ellipse, and jump from one ellipse to the next. Using the correct configuration one can also separate certain particles by changing the direction in which the field rotates. We have found that, in addition to ellipses, circular structures are also capable of trapping magnetic particles and be transported around their circumference. If two such circular disks of different diameters are adjacent to one another it would be possible to, not only trap magnetic particles on each circle, but also stretch a biomolecule such as a strand of DNA whose ends are attached to these magnetic particles. We will present our findings and a video showing the movement of the magnetic particles along specific directions on the platform.

Presenter: Rachel Mauk
Title: Late-season Tropical Cyclogenesis in the Northeastern Atlantic Ocean: 1975-2005
Advisors: Jay Hobgood
Department: Geography
Abstract:
    In the past thirty years, twenty named tropical cyclones formed in the northeastern Atlantic Ocean in the months of October, November, and December. By the accepted definition of a favorable environment for tropical cyclogenesis, most of them should not have developed. The past seven seasons produced ten of the twenty, with 2001 and 2005 generating three and four systems, respectively. The study period begins in 1975, the year in which the Hebert-Poteat technique for satellite identification of subtropical systems was published. The northeastern Atlantic is defined as the portion of the Atlantic north of 20 degrees N and east of 60 degrees W. Purely subtropical storms are excluded from the study to focus on the conditions for tropical transformation. The climatology of the twenty late-season tropical cyclones (LSTCs) is discussed including the peak development periods, location, maximum strength, and type of non-tropical origin. LSTCs in this region arise from four unique origins, providing a method for classification. Type I originate as pre-existing, non-frontal and non-tropical cyclones. Type II systems develop along dissipating frontal systems. Type III develop directly from an occluded frontal cyclone, while Type IV have tropical origins. Thirteen of the twenty systems are Types I and II, and the remaining systems are split relatively evenly between Types III and IV. The environment of each LSTC is examined during the twenty-four hours prior to attainment of tropical storm status. Wind fields and sea surface temperatures are calculated on a 13x13 Lagrangian grid. Wind shear is calculated for the 850-200 hPa, 850-300hPa, and 850-500 hPa layers. The shear values are averaged on 3x3 and 1x1 grids for quantitative comparison of systems. The synoptic environments are visualized on a 41x21 Eulerian grid centered on (30 degrees N, 50 degrees W) beginning at thirty-six hours prior to the tropical designation; of particular interest are the locations of upper-level troughs, ridges, and upper-level cold lows. With these data the conditions conducive to the formation of LSTCs are analyzed.

Presenter: Doug Schaefer
Title: Where is the Higgs Hiding?
Advisors: Brian Winer and Richard Hughes
Department: Physics
Abstract:
    Since the 1960s, the Standard Model has guided Particle Physics and has done a remarkable job of modeling physical processes. In fact, every particle predicted by the Standard Model has been seen except one: the Higgs boson. The Higgs boson is a force carrying particle which can help to explain the origin of mass. The discovery of this particle will also complete the Standard Model. Therefore, one of the main focuses of Fermilab, which is located about 30 miles outside of Chicago, is to find the Higgs Boson. To find the Higgs boson at Fermilab, scientists use the Tevatron. Tevatron is a 28 km in diameter ring collider which accelerates and collides protons and anti-protons at a beam line energy of about 1 TeV/c2. This energy is high enough to produce particles which have not been seen since the time of the Big Bang. I work on one of the detectors on the Tevatron called the Collider Detector at Fermilab or CDF. On CDF, one of the main search strategies for the Higgs boson uses the WH production mode. In this channel, the W boson decays into a lepton (either electron or muon) and neutrino while the Higgs boson (H) decays into a bottom quark and an anti-bottom quark pair. The charged leptons can be accurately detected and measured, while the neutrino and the quarks are measured relatively poorly. This analysis attempts to estimate the neutrino transverse energy and then use this information to in turn correct the measurement of the quark energies. This method may allow a much more accurate determination of the Higgs boson mass in WH events. We present expected improvements in Higgs mass resolution.

Presenter: Michael Titus
Title: Nanocrystallinity and enhancing magnetism in soft Fe-Si-Nb-Cu alloy
Advisors: Ratnasingham Sooryakumar
Department: Physics
Abstract:
    Our study details magnetic measurements of a nano-crystalline soft magnetic material that belongs to the Fe-Cu-Nb-Si-B family. These materials exhibit magnetic properties of high magnetic saturation, low coercivity and low losses. These excellent properties are key for many electrical device applications in the frequency range of 15-50 kHz. The material is available as amorphous ribbons that were grown using a rapid solidification process. Upon additional heat treatment called annealing, the material transforms to a nano-crystalline state. The crystals are 10-100 nm was measured from X-Ray Diffraction (XRD) and help enhance the magnetic properties of the material significantly. Different conditions such as annealing atmosphere, temperature, and time of anneal affect its magnetic properties and allow them to be tailored for specific applications. Previous work of others has significantly covered annealing conditions of temperature and time. Our study emphasizes different annealing atmospheres and its effect on the material?s magnetic and crystalline properties. We utilize XRD patterns to estimate crystalline grain sizes as well as percent crystallinity of the material. Magnetic properties such as saturation magnetization and coercivity are measured using a Vibrating Sample Magnetometer (VSM). Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques are used to verify grain size and material composition of the crystallites. Initial conditions of annealing between 500-600 degrees Celsius resulted in a very distinct transformation from an amorphous to crystalline state. This transformation is apparent in XRD analysis where the amorphous material exhibits a broad hump, but after annealing, strong and narrow peaks appear indicating crystallinity. SEM analysis confirms the transformation as apparent by small crystallites forming in the annealed material whereas the amorphous ribbon shows no crystallites or grains in the images. VSM measurements give coercivities on the order of 10-50 Oe and grain sizes of 10-400 nm. When the conditions were changed to a special process, preliminary results show drastically lower coercivities of 0.1-1 Oe as well as crystalline grain sizes less than 10nm. Decreased crystalline grain sizes and coercivities allow for lower losses in technological applications such as transformers and will help increase the performance over what is currently commercially available. Possible reasons for the enhanced magnetic properties after annealing will be discussed.



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