Seismic or wavefield interferometry refers to a set of methods that synthesize wavefields between pairs of receivers, pairs of sources, or a source and a receiver, using wavefields propagating from and to surrounding boundaries of sources and/or receivers. Starting from cross-correlations of ambient seismic noise recordings, which provide the signal between two receivers as if one of them had been an active source, interferometric methods developed rapidly within the last decade, revolutionizing the way in which seismic, acoustic, elastic, or electromagnetic waves are used to image and monitor the interior of a medium. Only recently, an explicit link was found between the methods of source-receiver interferometry (SRI) and seismic imaging, a technique widely used in seismic exploration to map diffractors and reflectors in the subsurface, but also in more academic studies investigating, for example, deep crustal processes. This link is particularly interesting because SRI, in contrast to classical imaging schemes, does not rely on the single-scattering assumption but accounts for all multiple-scattering effects in the medium. While first non-linear imaging schemes based on SRI have been proposed, the full potential of the method remains to be explored and a number of open questions concerning, for example, the role of non-physical energy in interferometric wavefield estimates, require further investigation. The aim of this thesis is to gain more insight into the method of source-receiver interferometry in the context of wavefield construction and analysis in multiply scattering media, especially when theoretical requirements of the method (such as complete boundaries of sources and receivers, surrounding the medium of interest) are not met. First I analyse the single diffractor case using partial surface boundaries only. I find that only two out of eight terms of the SRI equation are required to construct a robust estimate of the scattered wavefield, and that one of these two terms is also used in seismic imaging. The other term provides a pseudo-physical estimate of the scattered wave; this is a new type of non-physical energy that emulates the kinematics of a physically scattered wave. I then proceed to a multiple scattering scenario, using the pseudo-physical term to predict the travel times and exact scattering paths of multiply diffracted waves. The presented algorithm is purely data-driven and fully automated and, as a by-product, provides a new tool to isolate primary diffracted waves from a complex multiply diffracted wavefield. Finally, the concept is expanded to multiply reflecting media. In reflection seismic data, multiply reflected waves should be removed prior to migration in order to avoid artefacts in the seismic image. I demonstrate how internal multiples can be estimated and attenuated using pseudo-physical energy constructed from SRI. Moreover, an explicit link is derived between the internal-multiple equation based on SRI and the internal-multiple equation derived from the inverse-scattering series (ISS), currently the most capable algorithm for internal-multiple attenuation. Using the insight provided by the SRI approach, I suggest an alternative equation that estimates internal multiples more effciently compared to the current method. Overall, this thesis improves our understanding of how physical, non-physical, and pseudo-physical wavefields are constructed in SRI, how new information about multiply scattered wavefields can be inferred, and how SRI relates to other methods of wavefield analysis, in particular seismic imaging and the ISS.

Magnetic deflection techniques have been employed to measure proton angular distributions from some (d,p) and (t,p) reactions. In many cases the distributions exhibit typical stripping patterns and their analysis in terms of plane wave and distorted wave theories of stripping has enabled spin and parity assignments to be made for a number of excited nuclear levels. These theories are briefly outlined in Chapter 1 of this thesis and the experimental procedures are described in Chapter 2. The (d,p) reaction has been studied at an incident energy of 3 MeV with target nuclei B¹⁰, B¹¹, C¹², C¹⁴ and O¹⁶ and an account of this investigation is given in Chapter 3. Although the plane wave theory gives a good account of the angular distributions corresponding to the low-Q transitions (say Q ≤ 2 MeV) it is not a good approximation for the high-Q transitions. This is in accord with Wilkinson's suggestion that distortion effects should be quite small even at low deuteron bombarding energies providing also that the reaction Q-value is low. Agreement with the high-Q ground state distribution for B¹¹ could only be obtained with distorted wave theory if a cut-off radius were used. This may indicate the need for taking into account finite range effects in this theory. The Se⁷⁶(d,p)Se⁷⁷ reaction has been studied at 7.8 MeV bombarding energy and eleven angular distributions corresponding to the ground and ten excited states of Se⁷⁷ have been analysed using distorted wave theory. This investigation is described in Chapter 4. Deuteron and proton elastic scattering measurements have also been made from Se⁷⁶ and Se⁷⁷, respectively. The optical model potentials required to describe the stripping distributions are found to be entirely consistent with those derived from the elastic scattering data. In Chapter 5 an account is given of a systematic study of the (t,p) reaction for target nuclei B¹⁰, B¹¹, C¹², C¹⁴, O¹⁸, Si²⁸, Si²⁹ and Ca⁴⁰. This investigation was carried out at triton energies between 8 and 13 MeV. In the majority of cases the angular distributions are observed to be strongly forward peaked and these have been analysed in terms of Newn's plane wave theory of double stripping. With the exception of the B¹⁰(t,p)B¹² and C¹²(t,p)C¹⁴ reactions the agreement in general is found to be very satisfactory. In addition to the ground state, nine excited states of B¹³ were observed and information on the spins and parities of six of them have been obtained. The excitation energies of only four excited states were previously known. C¹⁶ had not previously been observed and the present investigation has shown this to be stable by 4.25 MeV against neutron emission, in good agreement with the predicitons of Zel'dovich. The ground state was confirmed to be O⁺ and the first excited state at 1.753 MeV excitation is probably 2⁺. The delayed neutron emission for C¹⁶ has also been studied and its measured half-life found to be 0.74 ± 0.03 seconds. Angular distributions were measured for the ground and nine excited states of O¹⁸ and ground and four excited states of O²⁰. Only one state, at 4.45 MeV excitation in O¹⁸, could not be interpreted by a double stripping process. Spin-parity assignments from the reactions Si²⁸(t,p)Si³⁰, Si²⁹(t,p)Si³¹ and Ca⁴⁰(t,p)Ca⁴² are in good agreement with earlier measurements. The Be¹¹ nucleus has been studied using the Be⁹(t,p)Be¹¹ reaction at 6 and 10 MeV triton energies. This investigation is described in Chapter 6. At the higher bombarding energy six energy levels of Be¹¹ were observed and three of these were found to have natural widths in excess of 10 keV. Proton distributions were measured at both energies for the ground and first excited states. Their interpretation in terms of a double-stripping mechanism is complicated by the presence of large backward peaks but the distributions are not inconsistent with the spins of 1/2 ^- and 1/2 ⁺, respectively, predicted by Talmi and Unna. Angular distributions from the C¹²(t,α)B¹¹ reaction at 10 MeV triton energy were also studied in an attempt to obtain information on the spins and parities of some of the states in B¹¹ which are involved in the beta-decay of Be¹¹. In Chapter 7 an account is given of triton elastic scattering measurements made at incident energies 6.4, 6.8 and 7.2 MeV from C¹², O¹⁶, O¹⁸, F¹⁹ and Ca⁴⁰. Only the scattering from F¹⁹ and Ca⁴⁰ can be described by the optical model, although the optical parameters are ambiguous. The scattering distributions from O¹⁶ at all three energies exhibit large backward peaks suggestive of compound resonance scattering. Optical model parameters derived from the triton scattering data have been uesd by Rook and Mitra to analyse the proton distributions from Ca⁴⁰(t,p)Ca⁴², using distorted wave theory. A brief account of the results is given in Appendix C.

No description available.

The need of a working infrastructure in a city also requires an understanding of how the traffic flows. It is known that increasing number of drivers prolong the travel time and has an environmental effect in larger cities. It also makes it more difficult for commuters and delivery firms to estimate their travel time. To estimate the traffic flow the traffic department can arrange cameras along popular roads and redirect the traffic, but this is a costly method and difficult to implement. Another approach is to apply theories from physics wave theory and mathematics to model the traffic flow; in this way it is less costly and possible to predict the traffic flow as well. This report studies the application of wave theory and expresses the traffic flow as a modified linear differential equation. First is an analytical solution derived to find a feasible solution. Then a numerical approach is done with Taylor expansions and Crank-Nicolson’s method. All is performed in Matlab and compared against measured values of speed and flow retrieved from Swedish traffic department over a 24 hours traffic day. The analysis is performed on a highway stretch outside Stockholm with no entries, exits or curves. By dividing the interval of the highway into shorter equal distances the modified linear traffic model is expressed in a system of equations. The comparison between actual values and calculated values of the traffic density is done with a nominal average difference. The results reveal that the numbers of intervals don’t improve the average difference. As for the small constant that is applied to make the linear model stable is higher than initially considered.

This thesis describes the experimental investigation of three different strongly correlated transition-metal oxide systems. The magnetic behaviour of each has been probed using inelastic neutron spectroscopy. A distinctive hour-glass excitation spectrum has been observed in the layered cobaltate La_1.75Sr_0.25CoO₄. This spectrum is similar to that measured in a related cobaltate La_1.67Sr_0.33CoO₄, although it appears broader. The spectrum has been reproduced using a spin wave model derived from a disordered cluster spin glass ground state. Signatures of spin glass behaviour have also been observed in bulk magnetisation measurements of La_1.75Sr_0.25CoO₄. These findings, once more, demonstrate the emergence of an hour-glass spectrum from a ground state that combines quasi-one dimensional magnetic correlations and disorder. Additionally, this study shows that charge and magnetic stripe order persists to lower dopings in La_2-xSr_xCoO₄ than previously thought. The complete magnetic excitation spectrum of the multiferroic compound CuO has been measured for the first time. A high energy, one-dimensional magnetic spectrum is observed and modelled using the Muller ansatz derived for the S=1/2 Heisenberg antiferromagnetic chain. At lower energies, a three-dimension spectrum is observed. The measured spectrum is inconsistent with all previous theoretical estimates of the dominant inter-chain exchange interactions in CuO. The inter-chain dispersion is successfully described by a phenomenological model based on linear spin wave theory. The third material investigated, LuFe₂O₄ demonstrates complex charge and magnetic order, the precise nature of which is still under debate. The full spectrum of in-plane excitations in LuFe₂O₄ has been measured and a complicated dispersion consistent with six magnetic modes is observed. These findings are compatible with structures described by a magnetic unit cell containing six spins. The dispersion can be described by a spin wave model derived from a bilayer structure comprised of charge-rich and charge-poor monolayers. This structure is consistent with the original site-specific model for the 3D magnetic ordering in LuFe₂O₄.

Ph.D. / A comprehensive experimental study of the effects of the spin-density-wave (SDW) on the physical properties of antiferromagnetic , doped with Mn and V, and Cr-Re alloys is reported. The purpose of the study is twofold: c c Al Cr − 1 (i) To gain insight in the anomalous behaviour of the magnetic phase diagram reported for the binary Cr-Al system. (ii) To investigate SDW effects on the anharmonic behaviour of the lattice vibrations of Cr alloys with a member of the transition metals of group-7 in the periodic table. The investigation entails the following measurements: thermal expansion in the temperature range 77 – 450 K for all the specimens, velocity of sound in the temperature range 4 – 300 K for the Cr-Al-V alloys, ultrasonic wave velocity for the Cr-Re alloys as a function of applied pressure (up to 0.242 GPa) at different temperatures and electrical resistivity in the temperature range 77 – 450 K for the Cr-Re alloys. Concentration-temperature magnetic phase diagrams of the (Mn, V) alloy systems were constructed from the measurements. Alloying with Mn, to increase the electron concentration, is observed to drive an incommensurate (I) SDW alloy towards a commensurate (C) SDW state. This results in a triple point, where the ISDW, CSDW and paramagnetic (P) phases coexist on the magnetic phase diagram. A hysteretic first-order ISDW-CSDW/CSDWISDW phase transition line is then observed on the phase diagram for Mn concentrations above the triple point concentration. Adding V, in order to decrease the electron concentration, to an ISDW alloy is found to have the opposite effect. It drives such a system deeper into the region of the ISDW c c Al Cr − 1 c c Al Cr − 1 phase. A CSDW alloy is, on the other hand, driven towards the triple point by addition of V, instead of Mn. c c Al Cr − 1 Theoretical analysis of the magnetic phase diagrams of the (Mn, V) systems confirms a previous suggestion that the Al impurity acts as an electron acceptor in the Cr matrix for c c Al Cr − 1 2 < c at.% Al, as opposed to an electron donor for at.% Al. 2 > c The high-pressure ultrasonic studies on the Cr-Re alloys were used to construct their pressure-temperature ( T p − ) magnetic phase diagrams. Applying hydrostatic pressure to a CSDW Cr-Re alloy induces a hysteretic first-order CSDW-ISDW phase transition at a certain critical pressure, resulting in a triple point on the phase diagram. An interesting aspect of the observations on the Cr-Re alloys is the suggestion of a new phase line, separating pressureinduced and temperature-induced ISDW phases, on the T p − T p − phase diagram. Acoustic-mode Grüneisen parameters, which quantify the lattice anharmonicity, were calculated for the Cr-Re alloys from the high-pressure ultrasonic measurements. The results indicate exceptionally large interactions between the SDW and the long-wavelength longitudinal phonons in Cr-Re alloys. These effects are particularly large in the vicinity of the Néel phase transition temperature. Interactions of the SDW with the shear mode phonons are on the other hand relatively much smaller. The work on the Cr-Re alloys is considered to finally complete studies of the lattice anharmonicity of Cr alloy systems with elements of all the important groups of the periodic table. It now paves the way for developing microscopic theories to explain the unique behaviour of the magneto-elasticity of dilute Cr alloys. / Prof. H.L. Alberts Dr. A.R.E. Prinsloo

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Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 339-359). Also available via the Internet

Thesis (M.S.)--Wake Forest University. Dept. of Computer Science, 2004. / Includes bibliographical references (leaves 67-69).

Thesis (Ph. D.)--Florida State University, 2005. / Advisor: Dr. James S. Brooks, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Sept. 15, 2005). Document formatted into pages; contains xiii, 120 pages. Includes bibliographical references.