Physics
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/52
The Physics department is committed to education and research in physics, the study of the fundamental universal laws that govern the behavior of matter and energy, and the exploration of the consequences and applications of those laws. Our department is widely known for its excellent teaching and student mentoring. Our department plays an important role in the university’s Core Curriculum. We have strong academic programs with several options for undergraduate physics majors, leading to the B.S. degree, as well as graduate curricula leading to the M.S. and Ph.D. degrees. Our research groups span a variety of fields within physics. Our principal concentrations are in Astrophysics, Relativity, Gravitation and Cosmology, Condensed Matter Physics, Lasers and Optics, Physics Education, Solar Physics, and the Space Science and Engineering Lab.
Browse
27 results
Search Results
Item A practical method for determining pit depths using X-ray attenuation in EDX spectra(2015-04) Avci, Recep; Davis, Bret H.; Wolfenden, Mark L.; Kellerman, Laura R.; Lucas, Kilean; Martin, Joshua; Deliorman, MuhammedinA practical method has been developed for rapidly determining the depth of a corrosion micro-pit from the path lengths of X rays passing through the walls of the pit on their way to an X-ray detector. The method takes advantage of the attenuation of the Bremsstrahlung and characteristic X-ray radiation accompanying each X-ray spectrum, and the results are verified independently using AFM and the special pit geometry surrounding MnS inclusions in 1018 carbon steel. The method has general validity and is especially valuable in those cases where the pit depth-to-width ratio is too steep to measure using the conventional methods.Item Multivariate Classification with Random Forests for Gravitational Wave Searches of Black Hole Binary Coalescence(2015-03) Baker, Paul T.; Caudill, Sarah; Hodge, Kari A.; Talukder, Dipongkar; Capano, Collin; Cornish, Neil J.Searches for gravitational waves produced by coalescing black hole binaries with total masses ≳25M⊙ use matched filtering with templates of short duration. Non-Gaussian noise bursts in gravitational wave detector data can mimic short signals and limit the sensitivity of these searches. Previous searches have relied on empirically designed statistics incorporating signal-to-noise ratio and signal-based vetoes to separate gravitational wave candidates from noise candidates. We report on sensitivity improvements achieved using a multivariate candidate ranking statistic derived from a supervised machine learning algorithm. We apply the random forest of bagged decision trees technique to two separate searches in the high mass (≳25M⊙) parameter space. For a search which is sensitive to gravitational waves from the inspiral, merger, and ringdown (IMR) of binary black holes with total mass between 25M⊙ and 100M⊙, we find sensitive volume improvements as high as 70±13−109±11\% when compared to the previously used ranking statistic. For a ringdown-only search which is sensitive to gravitational waves from the resultant perturbed intermediate mass black hole with mass roughly between 10M⊙ and 600M⊙, we find sensitive volume improvements as high as 61±4−241±12\% when compared to the previously used ranking statistic. We also report how sensitivity improvements can differ depending on mass regime, mass ratio, and available data quality information. Finally, we describe the techniques used to tune and train the random forest classifier that can be generalized to its use in other searches for gravitational waves.Item Projected Constraints on Lorentz-Violating Gravity with Gravitational Waves(2015-04) Hansen, Devin; Yunes, Nicolás; Yagi, KentGravitational waves are excellent tools to probe the foundations of General Relativity in the strongly dynamical and non-linear regime. One such foundation is Lorentz symmetry, which can be broken in the gravitational sector by the existence of a preferred time direction, and thus, a preferred frame at each spacetime point. This leads to a modification in the orbital decay rate of binary systems, and also in the generation and chirping of their associated gravitational waves. We here study whether waves emitted in the late, quasi-circular inspiral of non-spinning, neutron star binaries can place competitive constraints on two proxies of gravitational Lorentz-violation: Einstein-\AE{}ther theory and khronometric gravity. We model the waves in the small-coupling (or decoupling) limit and in the post-Newtonian approximation, by perturbatively solving the field equations in small deformations from General Relativity and in the small-velocity/weak-gravity approximation. We assume a gravitational wave consistent with General Relativity has been detected with second- and third-generation, ground-based detectors, and with the proposed space-based mission, DECIGO, with and without coincident electromagnetic counterparts. Without a counterpart, a detection consistent with General Relativity of neutron star binaries can only place competitive constraints on gravitational Lorentz violation when using future, third-generation or space-based instruments. On the other hand, a single counterpart is enough to place constraints that are 10 orders of magnitude more stringent than current binary pulsar bounds, even when using second-generation detectors. This is because Lorentz violation forces the group velocity of gravitational waves to be different from that of light, and this difference can be very accurately constrained with coincident observations.Item Dielectric measurements of the proton-glass state in Rb0.65(NH4)0.35H2AsO4(1988-09) Trybuła, Z.; Schmidt, V. Hugo; Drumheller, John E.; He, Di; Li, ZhouningDielectric measurements of the Rb1−x/emph>(NH4)xH2AsO4 (x=0.35) mixed crystals in the a and c tetragonal directions in the temperature range from 3 to 300 K are reported. Below Tg a dielectric dispersion of ε’(T) and ε’’(T) in the applied frequency range from 1 Hz to 30 kHz was observed. A small anisotropy of the proton-glass transition temperature Tg was detected, but we did not find the large anisotropy reported by J. Kim, N. Kim, and K. Lee [J. Phys. C 21, L-663 (1988)].Item Cs 133 Nuclear Magnetic Resonance Study of One-Dimensional Fluctuations in CsH 2 PO 4 and Its Ferroelectric and Antiferroelectric Transitions at High Pressure(1989-02) Schuele, Paul J.; Schmidt, V. HugoPressure and temperature effects on the one dimensional (1D) and higher-dimensionality correlations associated with the ferroelectric and antiferroelectric phase transitions in cesium dihydrogen phosphate were studied by means of the Cs133 nuclear magnetic resonance (NMR) spin-lattice relaxation time T1. We measured T1 at 6.5 MHz at temperatures down to the ferroelectric (FE) Curie point TC at 1 bar and at 1.5 and 3.0 kbar, down to the triple point Tt=124.6 K at 3.3 kbar, and down to the antiferroelectric (AFE) Néel point TN at 3.6 kbar. With decreasing temperature, T1 first decreases exponentially due to 1D fluctuations associated with the Jb interactions in disordered hydrogen-bonded chains running along b. As the temperature falls further, T1 then decreases linearly as the Jc interaction between these chains in hydrogen-bonded planes comes into play. From these results and the known pressure derivatives of TC and TN, we calculated pressure dependences for Jb, Jc, and for the interplanar interaction Ja. At 3.3 kbar Ja changes sign, so the plane stacking becomes AFE instead of FE. Above 8.9 kbar, where Jc extrapolates to zero, a new AFE phase with a checkerboard arrangement of FE b chains is predicted.Item 17O NQR Study of the Antiferroelectric Phase Transition in TlH2PO4(1988) Seliger, J.; Zagar, V.; Blinc, Robert; Schmidt, V. HugoThe temperature dependence of the 1 7O NQR spectra in TlH2PO4 has been measured using a proton‐1 7 O nuclear quadrupole double resonance technique. The results show that the protons in the short one‐dimensionally linked O1–H1‐‐O1 and O2–H2‐‐O2hydrogen bonds are moving between two equilibrium sites above T c and freeze into one of the off‐center sites below T c . The protons in the asymmetric O3–H3‐‐O4hydrogen bonds are static and ordered above and below T c .Item Comment on “dielectric study of the ferroelectric transition of KH2PO4”(1976-08) Western, Arthur B.; Schmidt, V. HugoWe reanalyze a.c. dielectric data taken by Eberhard and Horn for KH2PO4 near Tc, and obtain a much lower value of the critical bias field, near 300 V/cm in accord with results found by other workers.Item Soft modes and proton tunneling in PbHPO4, squaric acid and KH2PO4, type ferroelectrics(1984-01) Blinc, Robert; Schmidt, V. HugoIt is pointed out that the huge observed differences in the soft mode frequencies of KH2PO4, PbHPO4, CsH2PO4 and squaric acid do not necessarily reflect a large difference in the proton 0—H———O tunneling frequencies but rather result from a difference in the short range correlations renormalizing the single proton O——H—O tunneling frequency.Item Slater-senko model for CsH2PO4(1984-04) Schmidt, V. HugoThis model for CsH2PO4 considers all six Slater H2PO4 configurations and employs the Senko long-range interaction to obtain a ferroelectric transition above 0 K. Model predictions are compared with experimental results for susceptibility, spontaneous polarization, and correlation length.Item EPR study of the symmetry breaking effect in ferroelectric cesium dihydrogen phosphate doped with Cr5+ ions(1984-11) Waplak, S.; Schmidt, V. HugoThe (PO4)3− units in a CsH2PO4 (CDP) crystal were replaced in a small fraction of sites by (CrO4)3− groups and the EPR of the Cr5+ center was investigated. Splitting of the EPR line appears at T∗c=245 K, 91 K higher that the ferroelectric transition temperature Tc=154 K. The electronic wave function of Cr5+ (3d1) is identified as dx2−y2. The dx2−y2 function couples with the near protons and the reorientation of this unit in the two possible configurations occurs in the paraelectric phase and breaks the symmetry far above Tc. The observed correlation time 10−9 sec and associated activation energy ΔU=0.215 eV are discussed.
- «
- 1 (current)
- 2
- 3
- »