Hundreds of years after exploding, the original light from a supernova can still be observed in the form of light echoes. This light scatters off interstellar dust and is re-directed back toward Earth; due to the extra travel time, we observe the echo after the initial outburst. At some time t after observing the outburst, the surface of equal travel paths defines an ellipsoid with Earth and the supernova at the foci. If dust intersects this ellipsoid it is possible to scatter the light and produce an echo. In this thesis, I develop a relative probability model for the detection of supernova light echoes based on the physical characteristics of interstellar dust and absorption near the Galactic plane. This model includes a dust scattering function, distribution (scale height) of dust in the Galaxy, the dilution of echo flux with distance, and absorption along the supernova-dust-Earth travel paths. I have tested the model's predictions against observations and compared it with a prior survey strategy based on IRIS (re-processed IRAS) maps. Currently the IRIS-based strategy is more effective at selecting good paintings but its detection rate is only around 5%, highlighting the elusiveness of echo appearances. This work considers six historical supernovae in the Milky Way, all of which exploded in the pre-telescopic era (with the possible exception of Cas A) and were recorded as "guest stars" in astronomy records from Asia, Europe, and the Middle East. Their light echoes could give us information on these historically significant events and an opportunity to simultaneously study a supernova in outburst and several hundred years later. Early investigations suggest that the distribution of CO in the Galaxy may anti-correlate with the best paintings for light echoes; if a CO-echo link can be established, this would be useful in future light echo surveys. / Thesis / Master of Science (MSc)

Foliage is very common feature in the habitats of echolocation bats and thus its echoes constitute the major input of bats' sensory systems. Acquiring useful information from vegetation echoes facilitates the bats significantly in the navigation and foraging behaviors. To better understand the foliage echoes, in this dissertation, a computer model was constructed to simulate foliage echoes with following simplifications: approximating leaves as circular disks, leaving out shading effects between leaves, and distributing leaves uniformly in the space. Then one tree can be described with three parameters in the model, leaf radius, orientation, and leaf density, where the first two determine the beampattern of each leaf. Compared with echoes collected from real trees, the simulation echoes are qualitatively accurate, i.e., they match in waveforms and also first-order statistics. Since the ground truth is known in the model, the three parameters were estimated with lasso model by selecting 40 features from each echo. The results have shown that estimation of one parameter with the other two known is usually successful with coefficient of determination close to one, and the classification still has reasonable accuracy when the number of known parameter is reduced to one. Besides, the three simplifications were examined with both experimental and simulation approaches. To assess the acoustic impact of leaf geometry on individual leaves, experiments were carried out by ensonifying leaves from both a single and different species. How the leaves' impulse responses change according to their equivalent radii was investigated. The simulation model of disks fits the experiments done with real leaves within one species and across species reasonably well. Shading effect is found to exist locally when two disks were 25 cm apart and were both in pulse direction. In addition, the inhomogeneous distribution of leaves was introduced by using the branching patterns of L-system. The evaluation of inhomogeneity in echoes produced with two distributions shows that there is always inhomogeneity in echoes, and L-system model does bring more inhomogeneity but not to the same extent as changes in the relative orientation between sonar beam and foliage do. / Ph. D.

Two different time-resolved spectroscopic techniques are discussed theoretically and demonstrated experimentally in dilute gases. The first technique involves extending the advantages of Stark-effect based time-resolved spectroscopy to non-polar molecules. This involves the development of a stable, TEM₀₀ mode, cw, CO₂ laser capable of switching rapidly and controllably between two frequencies. Design problems and output characteristics are discussed. The frequency switchable laser is applied to the CO₂ 10.6 μm P(16) coincidence with the non-polar molecule SF₆. The population relaxation time, T₁, is measured using two-pulse delayed nutation. The decay of induced dipoles is studied using the phenomenon of photon echoes. It is found that the echoes decay in a manner characteristic of dephasing dominated by velocity-changing collisions. A fit of the data to a model for such decays gives values of γ(ab) ≡ 1/T₂ (the non-velocity-changing contribution to the dipole decay rate), Γ(VC) (the total probability of a velocity-changing collision per unit time), and Δu which is related to the mean velocity change of SF₆ upon a velocity changing collision. A comparison with the published results of the similar Stark experiments on C¹³ H₃F are made. The second technique involves the development of an alternative to the pulsed excitation typically used in time-resolved T₁ studies. This involves inversion of a portion of the velocity distribution by adiabatic rapid passage (ARP) techniques. The center of this portion is then probed in the manner of previous delayed nutation experiments. The system preparation is shown theoretically to be different and simpler than the pulse case. In addition, ARP preparation gives a larger signal than two-pulse delayed nutation experiments. ARP experiments on N¹⁴H₃ and N¹⁵H₃ are described and compared to two-pulse delayed notation experiments. The single exponential decay best fits to the data from the two methods are found to be in agreement. We would expect the N¹⁵H₃ results to be very similar to the N¹⁴H₃ results, though reduced rotational resonance effects in its upper state should give it an overall slower decay. It is indeed found that the decay appears to be a simple exponential as did the N¹⁴H₃ data over the time range studied. The pressure dependent single exponential decay rate for N¹⁵H₃ is however roughly 45% larger than the rate for N¹⁴H₃ in the pressure range from 0.5 to 9 mTorr.

Coherent transient effects are the optical analogs of the many transient phenomena seen in pulsed nuclear magnetic resonance experiments on spin systems. For example, photon-echo and optical nutation are the respective optical equivalents of spin echo and transient nutation of nuclear magnetic resonance. In Stark-switching and frequency-switching techniques the laser field and the molecules are brought into resonance in a sequence of pulses, the rest of the time they remain well off-resonance. So far it has been assumed that the off-resonance field does not have any measureable influence on the experimental results and is utilized to implement a very efficient detection scheme. This work discusses how the off-resonance field affects the coherent transient effects. It is shown here how this field, by inducing changes in the index of refraction as small as 10⁻⁶ produces easily observable effects in photon echo and delayed optical nutation.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 142-145).

This thesis presents a new method to estimate the Apparent Proper Motion (APM) vector and its uncertainty for supernova light echoes (LEs) and tests its usefulness in practice on LEs due to two old Galactic supernovae (SNe) - Cas A and Tycho. Ten instances of two-dimensional cross-correlation (2-D CC) of images containing light echoes at diferent epochs are employed to examine how well this new method works in practice. The images selected for this work originate from KPNO 4m Mosaic 1.1 images and were originally processed by the Pan-STARRS pipeline. All the APM estimates reported in this thesis are within 1sigma of estimates based on supernova distance and age provided reasonable inclinations are assumed. It was found that several factors tend to reduce the expected precision of this method and these include: 1) the existence of more than one LE feature for each epoch, 2) longer intervals between the two epochs lead to a bias, and 3) the existence of dust filaments at more than one depth along the line of sight. The results of three LE fields which were in common with the previous studies by Rest et al. in 2008 and 2011, were compared and a good agreement was found between them in difference-images with the same time interval. Since pixel values have a significant role in the introduced method, a control region is considered to eliminate the defect of the irrelevant residuals to the LE features. Hence, the introduced method was not straightforward. In addition, this method was not thoroughly manual independent, as the benefits of the visual measurement from the previous method reported by Rest et al. (2008) and (2011) were adopted for this method. However, compared to the previous manual technique, there were much less manual measurements were taken for the whole LE features in one frame. Considering all the challenges, the CC method is favourable as the APM vector uncertainty can be determined, which has not been achievable with previous method before. / Thesis / Master of Science (MSc)

Four strangers are stranded in an old farmhouse by a winter storm. Gilley lives on the farm. Shadows move of their own volition on the farm, and Gilley talks to echoes and sees the dead reflected in mirrors. Gilley's husband, Frank, disappeared over forty years ago. Jason is a college student who seeks Gilley out for an interview. He agrees to help Gilley find Frank. Jesse is a young boy who finds his way to the house after an accident. August is a private investigator whom Jason calls for help in finding Frank. August does not have a shadow nor a reflection of his own, and he can't remember how he lost them. Each wants something that only the others can provide, but each wants to keep their own secrets.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 136-142). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 136-142). Also available on the Internet.

Recent evidence suggests that cardiac mechanics (e.g. cardiac strains) are better measures of heart function compared to common clinical metrics like ejection fraction. However, commonly-used parameters of cardiac mechanics remain limited to just a few measurements averaged over the whole left ventricle. We hypothesized that recent advances in cardiac magnetic resonance imaging (MRI) could be extended to provide measures of cardiac mechanics throughout the left and right ventricles (LV and RV, respectively). Displacement Encoding with Stimulated Echoes (DENSE) is a cardiac MRI technique that has been validated for measuring LV mechanics at a magnetic field strength of 1.5 T but not at higher field strengths such as 3.0 T. However, it is desirable to perform DENSE at 3.0 T, which would yield a better signal to noise ratio for imaging the thin RV wall. Results in Chapter 2 support the hypothesis that DENSE has similar accuracy at 1.5 and 3.0 T. Compared to standard, clinical cardiac MRI, DENSE requires more expertise to perform and is not as widely used. If accurate mechanics could be measured from standard MRI, the need for DENSE would be reduced. However, results from Chapter 3 support the hypothesis that measured cardiac mechanics from standard MRI do not agree with, and thus cannot be used in place of, measurements from DENSE. Imaging the thin RV wall with its complex contraction pattern requires both three-dimensional (3D) measures of myocardial motion and higher resolution imaging. Results from Chapter 4 support the hypothesis that a lower displacement-encoding frequency can be used to allow for easier processing of 3D DENSE images. Results from Chapter 5 support the hypothesis that images with higher resolution (decreased blurring) can be achieved by using more spiral interleaves during the DENSE image acquisition. Finally, processing DENSE images to yield measures of cardiac mechanics in the LV is relatively simple due to the LV’s mostly cylindrical geometry. Results from Chapter 6 support the hypothesis that a local coordinate system can be adapted to the geometry of the RV to quantify mechanics in an equivalent manner as the LV. In summary, cardiac mechanics can now be quantified throughout the left and right ventricles using DENSE cardiac MRI.