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Articles 61 - 90 of 118
Full-Text Articles in Physical Sciences and Mathematics
Modeling Scavenging For A Hydraulic Free-Piston Engine, Nathan Davies
Modeling Scavenging For A Hydraulic Free-Piston Engine, Nathan Davies
Macalester Journal of Physics and Astronomy
The hydraulic free-piston engine at the University of Minnesota offers a solution to improve the hydraulic efficiency and reduce emission output of off-road vehicles. We developed a MATLAB Simulink model to track the pressure, temperature, and mass profile of the fuel within the cylinder during operation. By varying different initial conditions of our model, we found that a higher intake manifold pressure and larger bottom dead center location results in higher scavenging efficiency. These results can be used to improve the controller of this engine and better maintain stable operation.
Band Extension And Possible Ridge Compression On Europa, Sarah Chinski
Band Extension And Possible Ridge Compression On Europa, Sarah Chinski
Macalester Journal of Physics and Astronomy
Jupiter's icy moon Europa has captivated and perplexed the scientific community since the discovery of its global liquid water ocean. Over the course of several missions to the Jovian system, high-resolution observations of Europa have determined that there are spreading zones where new crust is created, similar to the mid-ocean spreading tectonic process we observe on Earth. These features, known as bands, have symmetric hills and valleys, indicating brief events of activity where material from the interior is exuded through a central crack, and solidifies on both sides, creating two positive topography. Recently, Europan scientists have been questioning how these …
Electrical Measurement Of Sram Cell Variation And Sensitivity To Singe-Event Upsets By Low-Energy Protons, James M. Cannon
Electrical Measurement Of Sram Cell Variation And Sensitivity To Singe-Event Upsets By Low-Energy Protons, James M. Cannon
Macalester Journal of Physics and Astronomy
With the rise of the transistor in the 1970s, electronics shifted from analog circuitry, where values are stored on a continuum, to digital, in which ones and zeros are the law of the land. Transistors, as a class circuit element, can be affected by radiation and cosmic rays which then cause temporary or permanent failures, depending on the specifics of the situation. On Earth, this poses little risk with all electronics shielded by the magnetosphere, however for space bound electronics, the risks from these extraterrestrial particles are not so negligible. The first step in designing a mission to be able …
Design And Modal Analysis Of An Ultra-Wideband Receiver For Green Bank Observatory, Alyssa Bulatek
Design And Modal Analysis Of An Ultra-Wideband Receiver For Green Bank Observatory, Alyssa Bulatek
Macalester Journal of Physics and Astronomy
The next generation of radio receivers for astronomy will be marked by tenfold improvements in sensitivity. These sensitive receivers will be useful for the detection of broadband fast radio bursts and other transients as well as the efficient discovery of radio recombination lines among many other scientific pursuits. One contribution to these improvements is an increase to decade receiver bandwidths. The Green Bank Observatory (GBO) is currently in the process of fabricating a new ultra-wideband (UWB; 0.7 to 4.2 GHz) receiver for the Green Bank Telescope (GBT). The UWB receiver will be used by the North American Nanohertz Observatory for …
Alfalfa Harvest: Hi Imaging And 3d Modeling Of Candidate Local Group Dwarf Galaxies, Lilly Bralts-Kelly, Susie Paine, Elizabeth A. K. Adams, John M. Cannon
Alfalfa Harvest: Hi Imaging And 3d Modeling Of Candidate Local Group Dwarf Galaxies, Lilly Bralts-Kelly, Susie Paine, Elizabeth A. K. Adams, John M. Cannon
Macalester Journal of Physics and Astronomy
Isolated neutral hydrogen (HI) clouds, or "ultra-compact high-velocity clouds" (UCHVCs), form a small subset of detections by the Arecibo Legacy Fast ALFA (ALFALFA) blind extragalactic survey. These systems, if located within ~1 Mpc, would populate the lowest-mass end of the HI mass function. Subsequent optical imaging has revealed that some of these UCHVCs harbor associated (thought sparse) stellar populations, suggesting that they may be some of the most extreme galaxies known in the Local Volume, with properties akin to ultra-faint dwarf galaxies but with significant neutral gas reservoirs. In this work, we investigate the neutral hydrogen properties of six UCHVC …
Leoncino And Ugc 5186, Josh Bartz
Leoncino And Ugc 5186, Josh Bartz
Macalester Journal of Physics and Astronomy
AGC 198691 is commonly known as the Leoncino Dwarf and is one of the most metal poor galax- ies known. An Arecibo observation in 2011 first suggested that Leoncino could be gravitationally interacting with its neighbor UGC 5186. In this paper new VLA data is used to examine the H I com- ponent of both galaxies to determine their gravitational relationship. Although the VLA could not confirm intragalactic gas seen by Aricebo, the H I density and velocity components are strong indirect evidence of gravitational interaction. UGC 5186 has a large gaseous arm reaching in the direction of Leoncino. Additionally …
Haro 11, Pox 186, And Vcc 1313: The Enigmatic Behavior Of Hi Non-Emitters, Sarah H. Taft
Haro 11, Pox 186, And Vcc 1313: The Enigmatic Behavior Of Hi Non-Emitters, Sarah H. Taft
Macalester Journal of Physics and Astronomy
We present neutral hydrogen (HI) observations from the Very Large Array (VLA) telescope of the galaxies Haro 11, Pox 186, and VCC 1313. 24 hours of deep spectral line observation at the 21 cm line were obtained from the program 17B-287 of Haro 11, the primary galaxy studied in this capstone, and 176 and 203 respective minutes of archival VLA data at the 21 cm line were obtained from the program AS0832 of Pox 186 and VCC 1313, the secondary and tertiary sources of study for this capstone. Haro 11 is one of a very small number of local dwarf …
Binary Neutron Star Merger Rates. Predictions From Observations Of Dwarf Galaxies And Observable Rates With Ground-Based Gravitational-Wave Detectors, Karen Perez Sarmiento
Binary Neutron Star Merger Rates. Predictions From Observations Of Dwarf Galaxies And Observable Rates With Ground-Based Gravitational-Wave Detectors, Karen Perez Sarmiento
Macalester Journal of Physics and Astronomy
Binary Neutron Star (BNS) mergers are interesting events in the field of multi-messenger astronomy since they are sources of detectable gravitational wave signals and electromagnetic transients. Here I introduce a new method to calculate a conservative, lower-limit for the rate of BNS merger events that is proportional to the stellar mass and is based on evidence of an r-process event in the dwarf galaxy Reticulum II. Two estimates of the stellar mass in the nearby universe were made using a Schechter Mass Function and a modified version of the 2MASS Extended Source Catalog (2MASS XSC). The BNS merger event rates …
Uv Led System For Pl Measurements On Gan Samples, Dona H. Pantova
Uv Led System For Pl Measurements On Gan Samples, Dona H. Pantova
Macalester Journal of Physics and Astronomy
Gallium Nitride materials are direct bandgap semiconductors with important applications, such as in the production of light-emitting diodes and transistors. The process of photoluminescence, in which excited electron and holes emit electro-magnetic radiation when they recombine, can be used to study the structure and quality of Gallium Nitride materials. Due to the size of the bandgap in these materials (3.4eV), ultraviolet light is required to create electron-hole pairs in GaN. We designed and built a system, which uses ultraviolet light, to take measurements on GaN samples provided by a local company, Lightwave Photonics, who were interested in the quality of …
Investigation On The Electrical Properties Of Cdo/Zno Thin Films Using Thz Spectroscopy, Ramon Molina
Investigation On The Electrical Properties Of Cdo/Zno Thin Films Using Thz Spectroscopy, Ramon Molina
Macalester Journal of Physics and Astronomy
In this work, we study the electrical properties of transparent conducting oxides using physical and optical techniques. The objective is to characterize the conductivity of a series of cadmium oxide zinc-oxide thin films with varying cadmium concentrations using three methods. The Hall Effect estimates carrier concentration, sheet conductivity, and carrier mobility. Optical methods, such as FTIR spectroscopy, can provide estimates of the plasma frequency, which describes a metal’s transition from being transparent to opaque to light. THz spectroscopy extracts the complex conductivity of materials in the far infrared spectrum and provides insights on the optical transport properties of conductors. Our …
Understanding Solar Activity During The Last 400 Years, Sam Q. Hollenbach
Understanding Solar Activity During The Last 400 Years, Sam Q. Hollenbach
Macalester Journal of Physics and Astronomy
The solar cycle has a profound effect on both terrestrial and extra-terrestrial operations. Understanding the history of the solar cycle is necessary for studying long term trends, however older data is difficult to calibrate due to the sparsity of observations. In this paper we propose a new method for calibrating sunspot number data that does not rely on observational overlap. Initial testing shows promise in this method’s success, though more work must be done to ensure calibration consistency across all observers.
Recent Evolution Of The Eta Carinae Supernova Imposter System, Greta L. Helmel
Recent Evolution Of The Eta Carinae Supernova Imposter System, Greta L. Helmel
Macalester Journal of Physics and Astronomy
The supernova imposter Eta Carinae and its surrounding Homunculus reflection nebula have been of great interest for the last several decades. As the most massive star known in our Galaxy, this object is of particular importance in understanding high mass loss episodes and final stages in the evolution of other similarly massive stars in the later stages of their lives. Observations using the STIS CCD Instrument have been taken over the past 20 years for both the central star and the Homunculus as part of the Hubble Space Telescope (HST) Treasury Program on Eta Carinae. Recent changes in …
The Neutral Hydrogen Kinematics Of The Dwarf Galaxy Merger Ngc 3239, Robert N. Ford
The Neutral Hydrogen Kinematics Of The Dwarf Galaxy Merger Ngc 3239, Robert N. Ford
Macalester Journal of Physics and Astronomy
We present H I spectral line images of the nearby dwarf galaxy NGC 3239. The galaxy’s curious morphology suggests that it is a post-merger system. We propose that NGC 3239 is a merger because it has multiple tidal tails, an enhanced velocity dispersion throughout the disk, and widespread star formation. We have produced kinematic moment maps corresponding to the H I column density, radial velocity, and velocity dispersion. Further, position velocity (P-V) slices of the galaxy were taken and three-color images were made using the SDSS G, R, and I, filters for comparison with the moment maps. These slices illustrate …
Carrier Mobility Of Bismuth-Doped Perovskite, Kelly Flugaur-Leavitt
Carrier Mobility Of Bismuth-Doped Perovskite, Kelly Flugaur-Leavitt
Macalester Journal of Physics and Astronomy
As renewable energy increasingly becomes a priority around the world, the demand for inexpensive, efficient solar cells is greater than ever. Lead halide perovskites show promising potential, but have their share of drawbacks that could be improved through slight changes to its elemental composition. We used time-resolved terahertz spectroscopy to probe the differences created by doping lead halide perovskites with bismuth. We found that all samples, regardless of bismuth content, had a recombination time longer than one nanosecond, and that charge-carrier mobility decreased with the addition of bismuth.
Low Resolution Hi Imaging Of The Shield Galaxies, Masao L. Miazzo
Low Resolution Hi Imaging Of The Shield Galaxies, Masao L. Miazzo
Macalester Journal of Physics and Astronomy
We present low-resolution Karl G. Jansky Very Large Array D-configuration HI spectral line observations of 32 previously unobserved local-volume low-mass dwarf galaxies in the Survey of HI in Extremely Low-mass Dwarfs (SHIELD). SHIELD was designed to probe the physical characteristics of the objects that inhabit the faint end of the HI mass function as populated by the ALFALFA blind HI extragalactic survey. These low angular-resolution images localize the HI-gas and provide the first glimpse of the neutral interstellar medium in these sources. We quantify the total HI mass of each system, and, using SDSS imaging, we compare the HI and …
Actinometry Of Hydrogen Plasmas, A. M. Cotter, James Doyle
Actinometry Of Hydrogen Plasmas, A. M. Cotter, James Doyle
Macalester Journal of Physics and Astronomy
Optical emission spectroscopy (OES) can be used to map the electron energy distribution of hydrogen plasmas. Using actinometry, a type of OES where trace amounts of noble gases are introduced, the effect of discharge power on the electron temperature of hydrogen plasmas was explored. This was done using argon and krypton as actinometers for low pressure hydrogen plasmas. It was determined that the electron temperature decreased with respect to power supplied to the discharge.
Modeling Recombination In Solar Cells, Paul Chery
Modeling Recombination In Solar Cells, Paul Chery
Macalester Journal of Physics and Astronomy
Solar cells are a competitive alternative to nonrenewable energy sources such as fossil fuels. However, the efficiency of these devices is limited by photogenerated carrier recombination. We use a finite difference numerical model to study recombination phenomena in the absorber layer of solar cells including alternate recombination models and the effects of spatial distribution of recombination centers. We compare the effect of using the constant lifetime approximation for recombination to the full Shockley-Read-Hall expression in Silicon solar cells and find that the constant lifetime approximation holds for high defect densities but not for high photon flux densities. Finally, we simulate …
Physical Principles Governing Colloidal Particle Deposition At Low Reynold’S Number: Applications To Microbial Biofilms, Sophia Wiedmann
Physical Principles Governing Colloidal Particle Deposition At Low Reynold’S Number: Applications To Microbial Biofilms, Sophia Wiedmann
Macalester Journal of Physics and Astronomy
Biofilms formed from the adhesion of microbes to a surface hold great relevance to public health and wastewater management. However, the physical principles underlying the attachment stage of biofilm formation, when individual microbes first come into contact with a substrate, are not well understood. Here I report on a model of colloidal particle attachment to a surface that incorporates the effects of diffusion, advection, gravity, and the hydrodynamic lift and drag forces experienced by polystyrene beads at low Reynold’s number. The simulation predicts attachment rates of 1.04x10^(-8)m/s, 0.73x10^(-8)m/s, and 1.29x10^(-8)m/s for beads of radius 0.25 µm, 0.55 µm, and 0.90 …
Time-Resolved Thz Conductivity Of An Intermediate Band Semiconductor, Elliot Weiss
Time-Resolved Thz Conductivity Of An Intermediate Band Semiconductor, Elliot Weiss
Macalester Journal of Physics and Astronomy
Intermediate band materials have promising applications as affordable, highly efficient solar materials. However, intermediate band solar cells exhibit low efficiency to date. Carrier recombination is a critical process that limits efficiency. If electrons relax to the valence band before they can be collected, their energy is lost. To help understand the recombination dynamics and physical properties of intermediate band semiconductors, we obtain time-resolved THz conductivity measurements of the intermediate band semiconductor, GaPAsN, at various temperatures. From our results, we build a model that provides insight to the recombination dynamics of GaPAsN.
Almost Dark Galaxies: The Search For Optical Counterparts, Quinton O. Singer
Almost Dark Galaxies: The Search For Optical Counterparts, Quinton O. Singer
Macalester Journal of Physics and Astronomy
Presented in this paper are results from neutral hydrogen (HI) imaging and analysis of the "Almost Dark" galaxies AGC 219533, AGC 227982, and AGC 268363 using new, higher resolution observations from the Very Large Array (VLA). Selected from the ALFALFA survey, "Almost Dark" galaxies possess significant HI reservoirs but, when the HI data is compared to survey-depth ground-based optical imaging, their optical stellar counterparts have extremely low surface brightnesses. AGC 219533 is one such object. The other two sources, AGC 227982 and AGC 26833, were candidate dark galaxies, as no stellar counterpart was identified in initial ALFALFA optical matching, and …
Intervalley Scattering Rates In Tellurium Observed Via Time-Resolved Terahertz Spectroscopy, Joshua R. Rollag
Intervalley Scattering Rates In Tellurium Observed Via Time-Resolved Terahertz Spectroscopy, Joshua R. Rollag
Macalester Journal of Physics and Astronomy
We conducted time-resolved terahertz spectroscopy measurements on the elemental semiconductor tellurium. Pump-probe measurements were used to find the conductivity as a function of time in single crystalline tellurium samples. It was found that the excitation dynamics in tellurium changes for photon energies of 1.03 eV and 1.55 eV. The change in these excitation dynamics was attributed to intervalley scattering effects. A model using intervalley scattering and Auger recombination was fit to the data, giving a value of 2.28 ps for the intervalley scattering time constant in tellurium.
The Chiral Magnetic Effect In Heavy Ion Collisions From Hydrodynamic Simulations, Elias Lilleskov
The Chiral Magnetic Effect In Heavy Ion Collisions From Hydrodynamic Simulations, Elias Lilleskov
Macalester Journal of Physics and Astronomy
The quark-gluon plasma created in heavy ion collisions is an exotic state of matter in which many unusual phenomena are manifested. One such phenomenon is the "Chiral-Magnetic Effect" (CME), wherein the powerful magnetic fields generated by colliding ions spin-polarize chiral quarks, causing a net transport effect in the direction of the fields. The CME predicts specific charge-dependent correlation observables, for which experimental evidence was reported, although the evidence is subject to background contamination. Isobaric collision experiments have been planned for 2018 at RHIC, which will study this effect by comparing 96Ru-96Ru and 96Zr-96Zr collisions. The two colliding systems are expected …
Conductivity Measurements Of A Thermoelectric Nanomaterial Through Thz Spectroscopy, Michaela S. Koller, James Heyman, Gunnar Footh
Conductivity Measurements Of A Thermoelectric Nanomaterial Through Thz Spectroscopy, Michaela S. Koller, James Heyman, Gunnar Footh
Macalester Journal of Physics and Astronomy
In today’s society there is a great demand on energy output—in the United States alone we rely heavily on non-renewable energy sources. Thermoelectric materials may be able to be used to create more efficient energy systems or recover wasted heat from inefficient technologies. This paper focuses on the conductivity of a new thermoelectric material that incorporates copper into a tellurium nanowire PEDOT:PSS material. The addition of copper seems to increase the conductivity of the material, although the exact relationship between the percentage of copper to tellurium and its affect on the conductivity is uncertain from the results.
Transient Photoconductivity Of A Thermoelectric Nanomaterial Pedot:Pss With Tecu Nanowires, Gunnar J. Footh, Michaela S. Koller, James Heyman
Transient Photoconductivity Of A Thermoelectric Nanomaterial Pedot:Pss With Tecu Nanowires, Gunnar J. Footh, Michaela S. Koller, James Heyman
Macalester Journal of Physics and Astronomy
Thermoelectric materials are able to transfer heat energy into electrical energy. They have many important applications, and an increased understanding of them would allow the scientific community to develop more efficient thermoelectrics. We provide here transient photoconductivity measurements of a thermoelectric nanomaterial - PEDOT:PSS with TeCu nanowires on quartz substrate. Increased copper concentration in nanowires decreases photoconductivity in both transmission and reflectance measurements. Fermi blocking provides a reasonable explanation for this decrease in photoconductivity, which occurs when total nanowire mass approaches ~15% copper concentration.
A Direct Comparison Of Lyman-Alpha And Neutral Hydrogen Morphologies, Kathleen Fitzgibbon, John M. Cannon
A Direct Comparison Of Lyman-Alpha And Neutral Hydrogen Morphologies, Kathleen Fitzgibbon, John M. Cannon
Macalester Journal of Physics and Astronomy
The Lyman-Alpha Reference Sample (LARS) and its extension (eLARS) represent an exhaustive campaign to reverse-engineer galaxies. The main goal is to understand how \lya radiation is transported within galaxies: what fraction of it escapes, and what physical properties affect the \lya morphology and radiative transport (e.g., dust and gas content, metallicity, kinematics, properties of the producing and underlying stellar populations). Two galaxies from the sample, LARS02 and LARS09, were observed using the B and C configurations of the Very Large Array to examine the neutral hydrogen emission, which can be used to determine a galaxy's neutral hydrogen (HI) structure and …
Rotational And Hyperfine Analysis Of Aus, Ian A. Wyse
Rotational And Hyperfine Analysis Of Aus, Ian A. Wyse
Macalester Journal of Physics and Astronomy
Gas phase diatomic gold sulfide, AuS, was analyzed using optical spectroscopy. High-resolution spectra were collected and characterized and a global fit of the A2∑+-X2∏3/2 (0,0), B2∑–-X2∏3/2 (0,0), and C2Δ3/2-X2∏1/2 (0,0) transitions at 15570 cm-1, 16290 cm-1, and 17670 cm-1 was compiled and resulted in rotational constant determinations for the A2∑+((2σ)1(4π)4), B2∑–((2σ)2(4π)2(2σ*)1), and C2Δ3/2 …
Power And Langmuir Probe Measurements Of H2 Rf Plasma, Alexander A. Stowell
Power And Langmuir Probe Measurements Of H2 Rf Plasma, Alexander A. Stowell
Macalester Journal of Physics and Astronomy
Methane based gases are often used to produce thin films of biomaterials, such as diamond-like carbon, through Plasma Enhanced Chemical Vapor Deposition. The characterization of the H2 plasma will give a deeper understanding of the physical processes occurring. Understanding these processes could lead to the optimization of the production of these thin films in the future. In this paper, we examine the H2 plasma using a Langmuir probe to gain information on the electron temperature and density of the plasma discharge. We measured electron temperatures of 6eV. Our Langmuir probe data indicates the electron temperature remains constant as …
The Effects Of Hydrazine Monohydrate Surface Doping On Graphene, Christian M. Stewart
The Effects Of Hydrazine Monohydrate Surface Doping On Graphene, Christian M. Stewart
Macalester Journal of Physics and Astronomy
In this project we investigate how the carrier concentration and scattering time of chemical vapor deposition (CVD) graphene samples are affected by the exposure of these samples to hydrazine monohydrate. We used both immersion techniques and vapor deposition techniques to surface dope our graphene samples. We use both Fourier transform infrared spectroscopy and Hall effect measurements to investigate these effects.We find that after surface doping CVD graphene samples, the electron concentration greatly increases while the scattering time is nearly unaffected. We also find that this doping process with hydrazine monohydrate is reversible.
Increasing The Acceptance Rate Of H-> 4e- Run 1 Events By Relaxing The Applied Cuts, Beni J. Pazar
Increasing The Acceptance Rate Of H-> 4e- Run 1 Events By Relaxing The Applied Cuts, Beni J. Pazar
Macalester Journal of Physics and Astronomy
The Decay mode of Higgs into four leptons allows for accurate parameter reconstruction and is thus a useful channel to research. The study attempted to increase the number of four electron events that pass selection cuts, without greatly increasing the amount of background noise, by varying the transverse momentum, invariant mass of the subleading electrons, and electron identification. With the application of a boosted decision tree targeting the ZZ* noise, the study found that the optimal configuration was a loose electron identification with the invariant mass greater than 10 GeV and the transverse momentum greater than 7 GeV.
Contributing To Astropy: A Community Python Library For Astronomers, Asra Nizami
Contributing To Astropy: A Community Python Library For Astronomers, Asra Nizami
Macalester Journal of Physics and Astronomy
This paper discusses the author’s contributions to two packages affiliated with Astropy, a community Python library for astronomers. The packages the author contributed to were modeling, a sub-package within the core Astropy package, and WCSAxes, an Astropy affiliated package, outside the core package.