Physics and Astronomy Master's Thesis CollectionCollection of theses written by CSUN Physics and Astronomy department studentshttp://hdl.handle.net/10211.2/14032019-09-21T03:02:03Z2019-09-21T03:02:03ZMeasuring local spacetime curvature using GPS and GRACEGresiak, Keithhttp://hdl.handle.net/10211.3/1253012019-07-19T16:21:29Z2014-08-25T00:00:00ZMeasuring local spacetime curvature using GPS and GRACE
Gresiak, Keith
In this thesis the sensitivity of GPS and GRACE satellites to the local spacetime curvature was examined. Annual oscillations in a perturbation variable, β, in the Schwarzschild metric, as measured by GPS, used to express local position invariance (LPI) of fundamental constants was studied [15]. In this thesis these annual variations are modeled by extraterrestrial potentials. It was found that the solar tidal potential was the dominant effect and the influence of other planets was negligible. Looking at the contributions in the Fourier domain, it was seen that there were similarities in the periodicities of peaks at 180 and 365 days. The yearly peaks were found to coincide within 61.1% in amplitude. This is suggestive that the yearly and 180 day periods in are attributed to the solar tidal potential. Plotting the predicted β versus the measured β shows there is a linear correlation between the two with Râ� = 0.8980 and a slope of 0.7978. This shows evidence that GPS is sensitive to the local spacetime curvature. Since the solar tidal potential was left unfiltered from β, this thesis must reach the preliminary conclusion that GPS currently does not have sufficient accuracy for geopotential mapping of the earth's surface. To support ongoing efforts for the use of GPS for geodesy, geopotential mappings of the earth's surface were made using GRACE spherical harmonic coefficients. These were created using harmonics up to degree and order 50 and 100. The mappings represent a baseline for which to compare furture GPS mappings against. Weekly GRACE data was averaged and analyzed in the time and Fourier domains, as well as a function of longitude and lattitude, resulting in peaks that agreed favorably with the solar potential in periodicity, but not in amplitude. On average these peaks were found to be roughly one order of magnitude smaller than the solar tidal potential for GRACE. It is assumed this is due to the handling of the solar tidal potential in GRACE, but further study is needed.
Includes bibliographical references (pages 76-78)
2014-08-25T00:00:00ZAn approximate analytical solution for the excitation threshold in a one-dimensional Fitzhugh-Nagumo systemGreene, D'Artagnan G.http://hdl.handle.net/10211.3/1252932019-07-19T16:28:11Z2014-08-25T00:00:00ZAn approximate analytical solution for the excitation threshold in a one-dimensional Fitzhugh-Nagumo system
Greene, D'Artagnan G.
Understanding the nature of electrical excitation of a group of cells is important both in examining the onset of a cardiac arrhythmia and in designing the treatment for sudden cardiac arrest. In the past, several attempts have been made to understand the threshold for the excitation of a one-dimensional chain of cells from a mathematical viewpoint. However, obtaining an analytical solution to describe threshold phenomena has proven to be difficult as the equations in this problem are highly non-linear and resist solution by standard mathematical techniques. Here, we apply a method developed by Neu et al. where the time evolution of the width and amplitude of a pulse is approximately described by a gradient flow on a two-dimensional phase plane. Using this approach, we obtain a mathematical expression that successfully models the excitation threshold for an applied square current pulse in a simplified Fitzhugh-Nagumo system. We then analyze our solution to reveal how the excitation threshold depends on key physiological parameters.
Includes bibliographical references (pages 104-105)
2014-08-25T00:00:00ZChromospheric properties of the Sun as a starContreras, Luis Davidhttp://hdl.handle.net/10211.3/1212912019-07-19T16:21:18Z2014-06-04T00:00:00ZChromospheric properties of the Sun as a star
Contreras, Luis David
The chromospheric activity of the Sun is governed by the surface magnetic field often measured at the photosphere. We study the dependence of chromospheric activity on magnetic field of the Sun as a star by using observations by Integrated Sunlight Spectrometer (ISS) and Vector Spectromagnetograph (VSM) of Synoptic Optical Long-term Investigations of the Sun (SOLIS) instrument. The chromospheric activity is measured as the equivalent width (EW) of spectral lines in H-$\alpha$, He I 10830 nm, Ca II 854.2 nm, Ca II H and K, and Na D I 589.6 nm obtained with the ISS. The full disk mean total magnetic flux (FDMTMF) observed with the VSM is used as the measure of magnetic activity of the Sun. The equivalent width of Ca II K and He I 10830 nm measured by Livingston along with the Magnetic Plage Strength Index (MPSI) value and a Mount Wilson Sunspot Index (MWSI) obtained with 150-Foot SOlar Tower in Mt. Wilson Observatory are used to further study the relationship between the magnetic field and chromospheric activity.
Includes bibliographical references (pages 33-35)
2014-06-04T00:00:00ZLipid membrane-water partitioning of lysophospholipids and fatty acidsAlaee, Yasminhttp://hdl.handle.net/10211.3/1211832019-07-19T16:24:56Z2014-06-03T00:00:00ZLipid membrane-water partitioning of lysophospholipids and fatty acids
Alaee, Yasmin
The partition coefficients for the distribution of lysooleylphosphatdylcholine (LOPC) and oleic acid (OA) between water and dioleylphosphatidylcholine (DOPC) bilayer at temperatures of 5 C, 15 C, 37 C and 50 C were determined using a fluorescence assay. The enthalpy and entropy of the partitioning were determined from the temperature dependence of the partition coefficient. The Gibbs free energy decreases and entropy increases upon partitioning into the bilayer for both LOPC and OA, in the temperature region of study. The enthalpy changes of LOPC and OA partitioning are significantly different. LOPC partitioning into the bilayer is endothermic (increase in enthalpy) and OA partitioning is exothermic. This means that LOPC partitioning is entirely driven by entropy. Both enthalpy and entropy contribute favorably to OA partitioning into the lipid bilayer. Entropy contributions for both LOPC and OA are mainly due to the hydrophobic effect of the long hydrocarbon chains of these molecules. The difference between LOPC and OA in the enthalpies of partitioning is due to the difference in the polar characters of their head groups.
Includes bibliographical references (page 40)
2014-06-03T00:00:00Z