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Ashlie Burton (Capstone, April 2015, Advisor: Lawrence Rees )

Abstract

Prosthetic legs are very expensive, and persons with amputations in developing countries often don’t have access to prosthetic devices. 2ft Prosthetics researches low cost feet to give amputees an affordable option. One of the current designs is made out of layers of PVC. Amputees often complain that the foot is excessively loud during gait. To reduce this, we tested two different designs. One clinic in a developing country reported using an inner tube from a bike tire helped mute the sound. The second design tested used a screw drilled through the toe of the prosthesis to hold the layers of PVC together. To test the feet, we made multiple models of each design and tested them against the original PVC design. These feet were put on our testing fixture that compresses the toe and heel using two pneumatic pistons to simulate walking on the foot. While on the fixture, the sounds from these feet were recorded. We found the original, screw in toe, and tire design produced -27.2 dB, -31.0 dB, and -32.2dB of sound respectively during gait. The inner tube design was also tested for durability against the original design. Durability testing showed no significant difference between the durability of the two designs.

Daniel Eliason (Senior Thesis, April 2015, Advisor: Bryan Peterson )

Abstract

In this research, ionized boron carbide is used as the current choice ionic plasma. A powerful electric pulse must be generated to ionize and inject the sample into a cylindrical Malmberg-Penning trap, the goal being to approach the Brillouin density limit. Utilizing inductors and capacitors, a pulse forming network (PFN) was designed and made to provide a longer pulse to generate sufficient plasma. After further development of the PFN and insertion into the trap, the anticipated electrical behavior did not match the actual resulting waveform. The system and the PFN are being studied and will be modified to obtain correct functionality.

Stephen Erickson (Senior Thesis, April 2015, Advisor: John Colton )

Abstract

Nanostructured solar cells seek to surpass the present standards of efficiency and affordability in solar energy. The protein ferritin—a 12 nm diameter hollow sphere—serves as a unique template for synthesizing nanoscale solar energy materials. It allows for controlled and uniform nanocrystal synthesis, protection against photo-corrosion, and the ability to be manipulated into ordered arrays. In this thesis, I present a method of tuning the band gap of these encapsulated nanocrystals over a range of 1.60-2.38 eV by controlling their size and chemical composition during synthesis. Band gaps are measured using optical absorption spectroscopy to test the effects of these tunable parameters. Using just these materials, calculations indicate that the maximum solar energy conversion efficiencies under average sunlight could reach a high value of 38.0%. The addition of a material with a band gap similar to silicon (1.12 eV) would raise this maximum efficiency to 51.3%.

Adam Heninger (Capstone, March 2015, Advisor: )

Abstract

This capstone project is a study of the ability to predict the elastic curve of a cantilever beam with a point load applied at the free end using the Bernoulli-Euler beam theory together with strain measurements from a Fiber Bragg Grating (FBG). As our metric, we use the Bernoulli-Euler beam theory to calculate the change in the peak wavelength reflected by our FBG per change in strain of the FBG and compare this to the FBG strain coefficient given by the Butter-Hocker model.

Samuel Hord (Senior Thesis, April 2015, Advisor: Traci Neilsen )

Abstract

Ground reflections have a significant impact on the propagation of sound from a rocket firing. The impedance of the ground relies strongly on effective flow resistivity of the surface and determines the frequencies at which interference nulls occur. A softer ground, with lower effective flow resistivity, shifts the location of interference nulls to lower frequencies than expected for a harder ground. The difference in the spectral shapes from horizontal firings of GEM-60 rocket motors, over snowy and hard ground, clearly shows this effect and has been modeled. Different flow resistivity values yield reasonable comparisons to the results of horizontal GEM-60 test firings. A sensitivity analysis was performed to develop a method for obtaining reasonable flow resistivity values, with the results comparable to those supplied by the current literature.

Jared Jay (Senior Thesis, April 2015, Advisor: David Neilsen )

Abstract

We study the chaotic properties of the three-body problem in general relativity and examine the effects of successive post-Newtonian Hamiltonian correction terms. We set up a planar, two-parameter, three-body system consisting of a circular binary and an incoming star, and integrate the system many times, varying the two initial parameters by small amounts. We study the cases of equal masses and unequal masses. We observe that the initial parameter space contains regions of fairly predictable behavior and regions of chaotic behavior at all levels of approximation to relativity. This is strong evidence that the three-body exhibits the same chaos in general relativity as in Newtonian gravity.

Tyler Jones (Senior Thesis, April 2015, Advisor: Dallin Durfee )

Abstract

One type of color sensor made for consumer electronics uses an array of optically filtered photodiodes. The filters cause the photodiodes' measurements to depend on the wavelength and the intensity of the incident light. The relative amounts of light measured by each photodiode can then be used to determine the light's color. These sensors are made for use with broadband light, but the data sheet for one such sensor, the TCS3414, lists very few limitations on its capabilities, indicating that the sensor may be useful in laser spectroscopy. This document explores the TCS3414's performance in laser spectroscopy. Considerations such as algorithmic method, intensity, bit noise, and temperature dependence will be discussed. Measurements show that the sensor's measurements are repeatable and accurate to within less than 10 picometers for time scales on the order of a day. While this is not precise enough to directly find atomic transitions, it is precise enough to get the laser close enough to the transition that it can then be scanned to find the transition without mode hopping. It is also comparable to many mid-grade interferometers. Therefore, the sensor is viable as an alternative method for measuring laser wavelength for short time scales.

Brandon McKeon (Senior Thesis, April 2015, Advisor: David Allred )

Abstract

Silicon dioxide (SiO2) is useful in microelectronics, micro-fabrication and optics. It has traditionally been deposited through low-pressure chemical vapor deposition (LPCVD) at high temperatures (about 900 to 1000 C). Various reactants have been used in this process, such as dichlorosilane and oxygen, or silane and nitrous oxide in different combinations. We explore the reaction of dichlorosilane and nitrous oxide in SiO2 LPCVD by varying the temperature from 850 to 950 C and the pressure from 0.30 to 1.05 Torr. Films with mirror-like surfaces are deposited in an ambient temperature of 900 C, with a gas ratio of 3.33 parts nitrous oxide for every one part dichlorosilane, and at a pressure between 0.35 and 0.69 Torr, while pressures outside of this range result in foggy surfaces or no deposition. These results are in good agreement with previous work and indicate that careful control of pressure is necessary for depositing uniform films for use in optical applications.

Jerika McKeon (Capstone, April 2015, Advisor: )

Abstract

Simulations and other virtual teaching aids are relatively new to the classroom, and have had limited research on their effectiveness. This study was conducted as part of my student teaching experience and compared the educational effects of a class period using computer simulations compared to a one using traditional lab experiments. The students were given four multiple-choice questions before doing the lab, after the class period, and at the end of the unit. The data collected from student scores shows that while the students did learn from the lab, there was not a significant difference between the lab styles. However, the data comparing the two lab styles over time was barely below being significant. Further research could involve more periodic tests and tests some time after the unit was over to better measure the long-term retention rate between the lab styles.

Kyle Miller (Senior Thesis, April 2015, Advisor: John Colton )

Abstract

Electrons located in silicon vacancies of 4H silicon carbide (SiC) are potential spintronic devices. In our experiments, electron spin states are polarized with 870 nm laser light, and we manipulate the spins with resonant microwaves at 10.47 GHz and a magnetic field of 350 mT. Spin polarizations are detected by the change in photoluminescence from the silicon vacancy defects, and lifetimes are calculated via measurements of optically detected spin resonance and electron spin echo. We have measured T2 lifetimes in 10^14 cm^−2 proton-irradiated SiC to be about 16 μs between 6 and 295 K, fairly independent of temperature. A sample with decreased defect density, proton-irradiated at 10^13 cm^−2, had a lifetime of about 64 μs. A 10^17 cm^−2 electron-irradiated sample had a lifetime longer than we could measure. These results show that we can increase lifetime by varying defect concentration and type.

Chris Olsen (Senior Thesis, April 2015, Advisor: Justin Peatross )

Abstract

Within the semi-classical framework for strong-field laser harmonic generation, using Bohmian trajectories as radiation sources suggests emission of both even and odd harmonics. In contrast, using expectation values as the sources for Maxwell's equations predicts only odd-order harmonics, which are well known to emit coherently. We perform a photon-counting experiment to search for an incoherent second-harmonic signal, which is expected to be very weak. We constructed a spectrometer to detect hyper-Rayleigh scattering across second and third harmonic from helium. The third harmonic is found to have a superradiant enhancement. An upper bound on the strength of possible second harmonic is established assuming no subradiant suppression.

Nils Otterstrom (Senior Thesis, April 2015, Advisor: Dallin Durfee )

Abstract

Many physics laboratories rely on accurate wavelength meters for metrology applications. Unfortunately, traditional instruments for laser spectroscopy tend to be expensive and fragile. We demonstrate a method for laser wavelength metrology using a simple and inexpensive color sensor made of an array of filtered photodiodes. The photocurrents from photodiodes under four colors of filters are measured digitally using an external microprocessor. With this data, we calculate the wavelength of a laser using a set of calibrated spectral response curves and a least squares error algorithm. After analyzing and controlling thin film interference effects in the sensor, we report an accuracy of 0.0053 nm (on the range of 460.79 nm to 460.89 nm) and a stability of 0.0039 nm over 41.5 hours (at 460.85 nm).

Alex Safsten (Senior Thesis, April 2015, Advisor: Karine Chesnel )

Abstract

Magnetic domain memory (MDM) is the tendency of a magnetic material to recall its domain pattern after a disturbance resulting from an application of an external magnetic field. In general, magnetic materials do not exhibit this property, but some specialized thin films composed of layered ferromagnetic and antiferromagnetic materials do display magnetic memory. We measure the amount of memory of such films using the x-ray resonant magnetic scattering (XRMS) technique, and use a speckle-correlation technique to quantify the degree of magnetic memory in the sample. In particular, we examine how the magnetic memory in these films persists when we introduce an exchange bias between the ferromagnetic and the antiferromagnetic layers. We find that when bias is applied to the sample, the magnetic memory persists. However, the amount of memory and its behavior throughout the magnetization loop varies with the magnitude of the bias applied. We further find that the amount of memory and its behavior throughout the magnetization loop does not, however, vary much with multiple magnetization loop passes.

Elora Salway (Senior Thesis, April 2015, Advisor: Denise Stephens )

Abstract

The Hubble Space Telescope (HST) has observed a fair number of brown dwarfs which, in ground based images, appear to be single objects. Frequently, however, the higher angular resolution of HST reveals that some of these objects are binary systems. The small angular separation of these binaries hints that there may be many more unresolved binary brown dwarfs observed with HST. With Point-Spread Function (PSF) fitting, it is possible to identify binary brown dwarf candidates in the HST archives which are not visually resolved according to the Rayleigh criterion. By fitting a double PSF to each brown dwarf image in each filter and camera for which data exists, we can determine a range of fluxes for both components of the binary system. These fluxes will be used to constrain theoretical spectrum of brown dwarfs to the original data to find a range of temperature and gravity for both objects. This thesis presents the results of PSF fitting for the brown dwarf 2M 0559, which reveals the object to be a strong binary candidate.

Joseph Thaden (Capstone, April 2015, Advisor: Kent Gee )

Abstract

In high-amplitude noise propagation, as is the case with a military jet, nonlinear effects have to be taken into account. This paper will highlight and compare these nonlinear effects with those of geometric spreading and atmospheric absorption. Extensive measurements were taken, in April 2009, at Holloman Air Force Base, New Mexico during which one engine was cycled through four power settings while the other engine was set to idle. Measurements were conducted over five days during which atmospheric conditions changed significantly. Changes in temperature, humidity, ambient pressure, and wind speed affect absorption and other important acoustic variables, such as air density and the speed of sound. Although the changes were drastic over the course of a day, within a measurement period (typically thirty minutes), the changes are small enough that these variables can be treated as constants. This phenomenon allows researchers to successfully analyze the nonlinear characteristics of jet noise.

Cameron Vongsawad (Capstone, April 2015, Advisor: Traci Neilsen )

Abstract

Science Technology Engineering and Math education is increasingly important in our world as we continue to build a highly technical global society. I have sought to prepare myself to be an effective physics teacher and STEM educator with every opportunity I have been given throughout my education. The redevelopment of both a local BYU acoustics outreach program as well as a national outreach program for the Acoustical Society of America is what I have accomplished. My work has given me a better understanding of the use of pedagogy in a variety of educational setting including teaching sound to the deaf and hard of hearing as well as the use of demonstrations in education. My work has focused on understanding Utah Core Curriculum and implementing those parts that revolve around acoustics specifically for middle, and high school aged students as well as the general public. This work has prepared me to be an effective educator as I go forth to serve in public education as a high school physics teacher.

Daniel Woodbury (Senior Thesis, April 2015, Advisor: Scott Bergeson )

Abstract

We present the construction and characterization of a two-dimensional magneto-optical trap (MOT) as a source of cold calcium atoms. Atoms are cooled transversely from a hot effusive source and captured in the 2-D MOT without axial confinement. We present calculations for and creation of the calcium source, as well as calculations for a paired ytterbium 2-D MOT. The results demonstrate that the 2-D MOT is feasible for calcium, with atomic density reaching a peak of $1.3 \times 10^9$ atoms/cm$^3$ in the trap. While we predict these densities can provide a loading rate 25 times higher than loading directly from an effusive beam, we were not able to successfully create a 3-D MOT. We present possible reasons for these results, as well as our future plans for experimental development.

Katrina Wright (Senior Thesis, April 2015, Advisor: Denise Stephens )

Abstract

Brown dwarf spectra may be the result of binary systems. Because of this, two models must be combined and the models must be rebinned to the spectra to perform a best fit. Previous work has been in a less useful language and less general. This thesis describes the process of making code in C++ which can be used to fit any spectrum to the models.